Silicone Putty Seashell Mold for Kids

February 8, 2017

This is a fun and easy project to do with kids. You can simplify it by making it a simple one piece mold and/or leaving out the colorant. I find that seashells are an easy shape to mold from the silicone putty. Other small, simple shapes can work as well.

Materials needed:

  • AeroMarine Products Silicone Mold Making Putty
  • AeroMarine Products White Urethane Casting Resin
  • Urethane Colorant
  • Silicone to Silicone mold release (or petroleum jelly)
  • Plastic mixing containers and utensils
  • Gloves
  • Two small pieces of cardboard

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • Make sure everybody is wearing gloves.
  • Place your seashell on one of the small pieces of cardboard. The cardboard should be a few inches bigger all the way around than the seashell.

  • Separate out equal parts Silicone Putty Part A and Part B. This product isn’t especially fussy. You can measure out the parts visually and see that the two parts are approximately equal.

  • Use your hands to squish the two parts of Silicone Putty together, folding and mushing it until it is all mixed together and one uniform color.
  • Press the Silicone Putty over the seashell, starting at the top and smushing downward. Make sure to press around the edges of the shell. Don’t press down so much that that silicone becomes very thin. You want the silicone putty to be about a quarter inch thick.

  • Lightly press the second cardboard piece on to the top of the Silicone Putty. Thiscreates a flat spot for the mold to set on when its time to pour resin into the mold. It should look like a cardboard-silicone sandwich. Try to get the cardboard as even as possible.

  • Let the Silicone Putty cure for at least 20 to 30 minutes. This type of silicone (platinum catalyzed) can be affected by the cold, so if it’s chilly (under 68F), let it sit for a little longer.
  • After the Silicone Putty has cured, remove the top piece of cardboard and peel the mold off the bottom piece of cardboard.


  • If you are doing a one part mold, You can pull the shell out of the mold and skip ahead to the resin mixing and pouring part of this post.
  • For the two part mold, leave the shell in place. I usually cut some notches with an X-acto knife to help me line up the bottom and top parts of the mold. This isn’t 100% necessary. However, it does make it make it easier to line the mold halves up.

  • Next we need a silicone-to-silicone mold release to keep the two halves from sticking together. I used an aerosol called Petrolease, but plain petroleum jelly brushed on to the silicone works just as well. Make sure you get the mold release into the notches as well. You want a good barrier so that no part of the silicone will stick together.

  • Mix together another batch of the Silicone Putty and press it into the shell and onto the silicone, taking care that it fills any notches that you may have cut.
  • Let the silicone cure for 20 to 30 minutes. Once it is cured, separate the two halves and remove the seashell.

  • Measure out equal parts of Casting Resin Part A and Part B. If you are using colorant, add it to the Part B before you mix the two parts together. Mix well with plastic utensil/stir stick, scraping the sides and bottom of the mixing container.

  • If you are doing a one piece mold, pour the mixed Casting Resin into the mold, filling it up.

  • If you are doing the two piece mold, fill the mold cavity up about half way and then place the convex part of the mold gently on top, lining up the notches. A little Casting Resin will squish out of the Silicone Putty mold. That’s okay because this shows you that mold is completely filled. It is also why this type of mold is frequently called a squish mold.


  • Let the Casting Resin cure for at least 30 minutes, a little longer in colder weather. Then pop your new seashell out of your mold and trim away any flash.

  Here you can see the difference between the one piece mold and the two piece mold.

  • You can also multi colored shells by measuring out two sets of Casting Resin and adding to only one, or different colors to both.

  • If you can, have one person mix each color at the same time, or mix them very quickly, one after the other. Pour the colored casting resin into the mold at the same time. The slower you pour, the more swirled the colors will be. Just be mindful of the pot life.

You can use the Silicone Putty mold many times over to create an entire beach of seashells! You can find the products for this project and more information on our website,  You can always send us an email if you have any questions at




Food Grade Silicone Mold for Chocolate

January 25, 2017

In this post, we’ will make a multi part food grade silicone mold for chocolate. Our Food Grade silicone is FDA approved and is great for casting candies, chocolate, fondant, sugar and the like. It is not approved for use in ovens, however. For this project, we will use ice cube trays in fun shapes instead of already made original pieces. Sometimes, I find interesting molds that aren’t designed for what I want to cast into them, so I’ll go over how to cast a suitable material into the original mold to make a piece to cast from for the new mold.

Materials needed:

  • AeroMarine Food Grade Silicone Mold Making Rubber
  • AeroMarine Urethane Casting Resin
  • Urethane mold release
  • Ice cube tray of interesting shapes
  • Tupperware container, or other suitable plastic container
  • Scale
  • Mixing containers and utensils
  • Non-sulfur modeling clay
  • X-acto knife
  • Chocolate suitable for melting
  • Pam spray or butter
  • Food flavoring suitable for chocolate (optional)
  • Double boiler
  • Rubber spatula
  • Candy/food thermometer

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • Spray the ice cube tray(s) with the urethane mold release and let it sit for a few minutes. This allows the propellants in the mold release to evaporate, leaving behind just the mold release itself.

 Urethane mold release

  • Measure out the urethane casting resin. This material is mixed 1:1 by volume, so I just use solo party cups and pour the same amount of the A side and B side into two separate cups. Then I pour each cup into my clean, empty mixing cup and mix with a plastic utensil. Mix vigorously for about 90 seconds, taking care to scrape the sides and bottom of the mixing container. Then pour into the ice cube trays.

 Don’t worry about pouring perfectly, any flash can easily be trimmed away

  • After 30 minutes, the casting resin should be set enough to remove the pieces from the molds. Trim away any flash with an X-acto knife. I always make more pieces than I need for my mold so I can pick out the nicest looking ones.

  • After selecting your pieces, smush a little clay on to the bottom of each piece and press into the bottom of the Tupperware container. The clay will hold the piece in place so it doesn’t float when you pour the silicone. Remember to keep the pieces at least a half inch apart from each other and a half inch away from the sides of the container.


  • Weigh out the Food Grade silicone and catalyst. I weighed out 250 grams of Part A and 25 grams of catalyst. Pour the catalyst into the silicone Part A and mix thoroughly, until one nice uniform color (kind of a lilac/light pink).
  • Pick a spot in the mold box, not on the pieces, and pour high and thin to reduce air bubbles.


  • Let the silicone cure for 24 hours.
  • Once the silicone is fully cured, pull it out of the Tupperware. Sometimes this takes a bit of effort or an extra pair hands. Then pop the pieces out of the silicone. Trim any flash with an X-acto knife.

   Now we’re ready to make some chocolate!

  • I used a double boiler to melt and temper the chocolate. Tempering the chocolate is what makes it shiny and smooth, here’s a link for an easy how-to:
  • I added a few drops of orange extract to give the dark chocolate a little extra flavor, but that is optional.  You can add any flavoring you like.

 I used dark chocolate, but milk chocolate and semi-sweet will also work well.

  • I gave my mold a light spray with PAM to help the chocolate release from the Food Grade silicone mold. Then I pour the tempered chocolate into the mold and put it in the refrigerator to cool down.

 The candy thermometer is used to make sure the chocolate is the correct temperature to be tempered.

  • These took about an hour and a half to two hours to harden in the refrigerator. Once I          de-molded the chocolate, I cleaned my mold and melted and poured more chocolate. I kept the already made chocolate pieces in a bowl in the refrigerator.


That’s how we make lovely orange flavored chocolates for our loved ones for Valentine’s Day! The Food Grade Silicone can be wash with dish soap, dried, and stored in a zip-lock bag for future use. As always, if you have any questions, you can email us at

Curing Issues- Trouble Shooting

January 13, 2017

At some point, everybody mixes up some silicone or epoxy or urethane and it just doesn’t cure right. There are many things that can affect the curing process. This blog post isn’t meant to cover every thing that could possibly go wrong. These are some of the most common reasons for our products to have issues curing. As always, if you have any questions, send us an email at info@AeroMarine and we would be happy to help you.

 Curing problems common to all materials:

  • Ratios- Was the correct amount of Part A and Part B (or catalyst) used? Some materials need to be mixed by weight, some need to be mixed by volume. The Technical Data Sheet and the label on the front of the bottle will tell you the correct mixing ratio.
  • Mixing- Was the material well mixed? Our materials should be mixed by hand, using a wooden paint stir stick (silicones and epoxies) or a plastic mixing utensil (urethanes), taking care to really scrap the sides and bottom of the mixing container.  If your material cures hard in some spots and is tacky or soft in other spots, it is almost always because the material wasn’t mixed well enough.
  • Use by date- What is the use by date on the container? As we’ve covered in other posts, some materials go bad more quickly than others, while some remain viable, under certain conditions, past the use by date. Always check the use by date if the product has been sitting on your shelf for a while and mix a small test batch if it is past the use by date.

The use by date is shown here on the fourth line of the label, under the cure time.

Curing problems common to silicone:

Tin catalyst silicone (128,125, and 115 translucent silicone):

  • Dry weather- Tin catalyzed silicones are condensation cure, meaning they pull moisture from the air as part of the curing process. If the weather or environment is very dry, it can affect the cure time. If you can increase the humidity in the area where it is curing, that will help.

 The humidity is at 68%, which makes it a good day to work with tin catalyst silicone.

  • Cure inhibitors- Sulfur containing clay and latex gloves are the most common cure inhibitors for these types of tin catalyzed silicones. Check that any clay you are using does not contain sulfur and make sure the gloves you are wearing are not latex gloves.
  • Catalyst issues- For the 128 pourable and brushable silicones as well as the 115 translucent silicone, the catalyst will separate if it sits for more than a few hours. Therefore, it needs to be shaken vigorously before use.
  • Additives- Different additives (silicone diluent, silicone thickener, silicone accelerator) need to be added to either the silicone Part A or the catalyst to work. The Technical Data Sheet will tell you which part and how much to add.

Platinum catalyst silicone (Food Grade silicone, silicone putty, and 150 potting and high temp):

  • Cure inhibitors- Platinum catalyzed silicone has many cure inhibitors. The most common cure inhibitors for platinum catalyzed silicones are: tin (tin catalyzed silicone), sulfur, latex, alcohol, ethanol, methanol, ethyl acetate, vinyl acetate, melamine, amines and nitriles. Most of these are listed in the Technical Data Sheet. If you have questions, please give us a call.
  • Catalyst- Always shake the catalyst thoroughly before use.
  • Cold weather- platinum catalyzed silicones are addition cure and can be affected by lower temperatures. Warm up your work area if possible to help it cure in a timely manner.


  • Cure inhibitors- Once again, sulfur containing clay can cause curing issues.
  • Application- Latex needs exposure to air to cure. Too thick of a coat will cause the latex to take a very long time to cure, and if it’s much too thick, it might not completely cure at all. Apply the latex in very thin coats for best results.

 A nice thin, quick curing coat of latex.

 Too thick a coat of latex, lots of bubbles, it will take forever to cure, and it might not cure all the way through.

  • Cold weather- Cold temperatures can also slow the cure time. A heat gun can be used to speed up the dry time, just make sure to use it on the lowest setting, keep it at least 8 inches away from the latex, and keep it moving. You can also set the piece out in the sun or raise the temperature of the room where you are working  to 72F.

Urethane (rubber and casting resin):

  • Cure inhibitors- Again, sulfur containing clay can affect the curing process.
  • Shake Well- Both the A and B sides of these materials should be shaken well prior to mixing, especially the urethane rubber.
  • Cold weather- Urethanes do cure more slowly in colder weather. If possible, warm up your working area to 72F or set the bottles in the sun for 10-30 minutes before use. If pouring the urethane into a mold or form, make sure the mold/form is warmed up as well.
  • Batch size- Smaller batches (especially smaller than 6 oz) cure more slowly than larger batches, as do thinner pours that have a lot of surface area to let off heat. Warm the material, warm the work area and just be patient. It will cure eventually.


  • Double mix and pour- Because both epoxy resin and hardeners are both clear, it can be difficult to tell if the material is well mixed, which is why we recommend using the double mix and pour method. To do this, measure out your epoxy and hardener and pour them into a clean mixing container. Mix well for for a few minutes, taking care to scrape the sides and bottom of the container. Don’t whip or beat the epoxy because that will create air bubbles. Then pour the epoxy/hardener into a new, clean mixing container and mix for a few more minutes. From there, you can pour or brush or roll the material on as desired.
  • Cold weather- The epoxy curing process slows down at 65F and decreases very dramatically under 50F. Warm up the materials and your work area to 72F and be patient. It will cure eventually.
  • Batch size – Smaller batches (under 8oz) cure more slowly. Same as with cold weather, warm things up or be patient.

These are the more common issues that can affect the curing process for the various materials we carry. For more information, along with Technical Data Sheet for all the materials we have, please go to our website,



5 Frequently Asked Molding and Casting Questions

December 27, 2016

Here are 5 questions that we get asked on a weekly basis. As always, if you have any questions, you can contact us at

  • How do pick what type of material will be best to make my mold?

The type of material you will make your mold from depends on what you will be casting into the mold. Are you replicating a garden gnome and casting in concrete? Are you making chess pieces and casting in a urethane resin? Are you making candles and working with wax? The end product is what determines the molding material to use.

For concrete, Plaster of Paris, and Hydrocal, liquid latex is what you would use for a brushable mold. Our 75A urethane rubber would be used if you wanted to make a pourable block mold. The reason for this is the abrasion resistance of the latex and and urethane rubber. These materials are able to withstand repeated castings of coarse materials.

If you are going to be casting with an epoxy resin, urethane resin or wax, you will want a material like silicone mold making rubber that has a good heat resistance as all of those casting materials are warm to hot while curing.

The other general rule of selecting a molding material is the hard/soft dynamic between the casting material and mold. If you are going to be casting a hard part (most common), you want the mold itself to be soft and flexible. That way, the mold will give and flex for the part to come out. If you want your piece to be cast from a soft material, like a silicone, you would want the mold to be more rigid and the part will flex to come out of the mold. It is extremely difficult to remove a hard cast from a hard mold or a soft part from a soft mold. There are some exceptions to this rule, mostly when working with fiberglass and resin, but it is a good rule of thumb.

  • What is the shelf life of my product?

All of products have a use by date printed on their label. This is usually six months from the packaging date. That is how long we expect the product to reliably last. However, some products may last longer on the shelf than others.

128 Silicone with pourable or brushable catalyst- The white silicone base will last at least six months if stored in a closed container in a room temperature (68-72 F) environment. Sometimes it can last up to year, if it isn’t opened and closed too often. By 18 months it is usually too viscous to work well. The catalyst has a similar shelf life, always good up to six months, sometimes lasting up to a year.

125 Silicone, simple 1:1 mix ratio- This silicone will last on the shelf, UNOPENED, for six months. However, once you open this product and expose the “A” side to air, it needs to be used within sixty days. This is because the catalyst is in the “A” side and it will start to cure slowly once opened.

Latex-  If stored in a closed container in a room temperature environment, the mold making liquid latex will last at least six months, sometimes 12 to 18 months. However, if latex gets too cold, it will be ruined. Do not store the latex in environment where it will get below 50 F. So unheated garages and sheds during the winter and fall months are not a good idea. If your latex looks chunky, like cottage cheese, it has gotten too cold and needs to be thrown out.

Urethane Casting Resins- If stored in an air tight container, it will last six months. Urethane is very moisture sensitive before it is are mixed and cured, so using it on a rainy or humid day, using paper or wood mixing utensils and/or containers can cause moisture contamination that leads to bubbles in the urethane. You can make sure your casting resin lasts by using a dry gas nitrogen blanket (like X-Tend it) to displace the air in the bottle after every use.

Epoxy Resins- Epoxy resins and hardeners can last for years on the shelf. We label it with a six month use by date, but it doesn’t really go bad. Sometimes the resin side will freeze (at about 50 F) and become crystallized and cloudy looking, but it just needs to be warmed up to return to its former clarity with no impact on the resin’s strength and durability. The 21 hardener will darken over time, turning more yellow. This is purely a cosmetic issue which doesn’t affect the strength or durability of the final product.

With all of these products, if it is past the use by date on the label, a small test batch will tell you if the product is viable.

  • How should I store my molds when not in use?

Molds should be stored in a room temperature (68-72 F) environment, out of direct sunlight, in an air tight bag or container. If possible, it always best to store the mold with a cast piece in it. Glove molds should be stored with their mother molds in place. Latex molds are especially sensitive to heat and should never be stored anywhere where the temperature could reach over 72 F.

  • How long will a mold last?

Production life ( the amount of casts you will get from a mold) is hard to predict. Things that affect production life include:

Mold release will prolong the life of your mold, especially if used every time you do a cast.

Detailed and/or complex molds don’t last as long as simple molds.

Molds stored properly will last longer than molds just tossed on a shelf.

The materials used in the molds will also contribute to production life. Generally the hotter the casting material becomes while curing, the harder it is on the mold. Also more abrasive materials will wear the mold out faster.

Library life (how long a properly stored mold will last when not in use) is easier to predict and are as follows:

Tin catalyst silicone molds (like our 125 or 128 silicones) last about 5-7 years when stored properly

Platinum catalyst silicone molds (like our Food Grade silicone or silicone putty) last 20+ years when stored properly.

Latex molds last 10-20 years when stored properly.

Urethane rubber molds (like our 75A urethane rubber) last 20+ years when stored properly.

  • Can I color or paint the urethane casting resin?

Yes, our urethane casting resin can be colored. We carry white, black, red, yellow, and blue colorant for the casting resin. Any colorant for use with urethane will work with our casting resins. People frequently use powdered pigments and dyes in the casting resin. Always mix up a small test batch to make sure you are getting the color and result you want.

The casting resin can also be painted. For best results, dust or submerge your part in talc for 12 to 24 hours, and then wash with a liquid dish soap (like Dawn) with cold water and pat dry. Do not sand after the talc and washing. Some people also like to use a primer such as Plasti-Kote, a sandable primer that works well and can be found at most auto supply stores. Acrylic paints work very well. Other types of paints should be tested first. For a spray paint, Krylon Fusion works great.

Hopefully this information has been helpful to you.

From all of us at AeroMarine Products, have a lovely holiday!



Mold and Cast An Epoxy Glitter Ornament

December 21, 2016

For this project, I made an epoxy and glitter ornament. The original piece was sculpted from modeling clay. The silicone mold is a simple one piece block mold. The epoxy and glitter was poured in layers to give the finished product dimensionality.

Materials needed:

  • AeroMarine 300/21 Epoxy Resin
  • AeroMarine Products 128 Pourable Silicone
  • Modeling clay
  • Cardboard
  • Hot glue gun
  • X-acto knife
  • Small, inexpensive paintbrush
  • Epoxy mold release
  • Glitter
  • Scale
  • Level
  • Gloves
  • Thin ribbon

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • To start, I cut out a piece of cardboard a  bit larger than I wanted the ornament to be. I sketched out an outline of the shape I wanted sculpt. I used medium non-sulfur plasteline clay to sculpt the ornament shape. I should mention I did not go to art school and I have no formal training in sculpture so I tend to stick to basic, simple shapes if I need to sculpt an original. I say this because many people are intimidated by trying to sculpt a shape for an original and they needn’t be. However if you don’t want to sculpt the shape yourself, you can frequently find pre-cut wooden shapes at a craft store or even a cookie cutter that you could use to cut out the shape from rolled out clay.


  • Next, I cut cardboard for sides of the mold box and hot glue them into place around my clay original. Remember to keep the sides a half inch to an inch away from the piece.

  • I used AeroMarine 128 Pourable Silicone to make the mold. I have covered the mixing and pouring of this product in more detail in the previous post about the two part pumpkin mold. For a brief recap, make sure your work surface is level before you pour, mix the silicone 10:1 by weight (I use a scale that weighs grams) with the catalyst and mix until it is an uniform color. Don’t forget to scrape the sides and bottom of your container while mixing.
  • Since the ornament has some detail where the top meets the round part, before I poured the silicone, I used a brush to work a bit of the silicone into the detail part. This helps ensure that the silicone gets into the detail area with no air bubbles. You should use an inexpensive brush for this because silicone can be difficult to remove fully from the bristles.

  • Once the silicone is poured, let it cure for 24 hours. Then take it from the mold box and remove the clay original from the mold. Find the most level area of your work space and place the mold there. An inexpensive level from Target or Home Depot will help you find the best spot to place your mold.
  • I sprayed a light coating of Epoxy Mold Release into the silicone mold before I started measuring and mixing my epoxy. This  helps the finished casting pop easily from the mold. Using a mold release saves wear and tear on the mold and prolongs the life of the mold.
  • I used AeroMarine Products 300/21 Clear Epoxy Resin to pour into the mold. This product has a 2:1 by volume mix ratio. I used very small Solo cups to measure out 2 parts 300 resin and 1 part 21 hardener. You cannot vary the mix ratio with this product to speed up or slow down the cure process. It has to be mixed 2 parts of 300 resin to 1 part of 21 hardener for it to cure properly. I used a disposable plastic knife to mix the the combined 300 resin and 21 hardener.


  • For the first pour of resin, I just want to coat the bottom of the mold with a thin layer of epoxy. I want to layer the epoxy and glitter because the glitter tends to settle at the bottom of the epoxy and it doesn’t look as nice.

  • After the first pour of epoxy is tack free, that is, it doesn’t come away on your finger if you touch it (about 12-24 hours), then do the next pour. First, I sprinkled some red and green craft glitter into the mold.

  • Next, I mixed and poured the next layer of epoxy, filling the mold up about halfway.

  • After that layer of epoxy cured, I sprinkled some silver glitter into mold. Then I mixed and poured the next layer of epoxy, almost filling it to the top, but leaving room for one more thin pour.

  • Once that layer has cured, I mixed up and poured the final, thin, plain layer of epoxy. This just ensures that there are no glitter bits poking out, everything is totally encased in the epoxy.
  • After waiting 24 hours for the epoxy to cure, popped the ornament out of the mold. Because the clay wasn’t as smooth as it could be, the epoxy appeared a little frosty. Fortunately this is very easy to fix. I mixed a small amount of epoxy and brushed a thin coat on.

  • Once the epoxy cured the ornament had a high gloss finish and you could see all the glitter suspended within it.

  • Tie a short length of ribbon through the hole on top and it’s done.

I did an ornament shape with glitter for this project.  However, you can do any any shape and embed a variety of things in the epoxy like pictures, bottle caps, coins, etc, by following the same basic steps. If you are embedding paper products, they must be sealed with a clear urethane or acrylic sealant first. Otherwise, the epoxy will give the paper a “wet” look. If you have any questions, you can always contact us at!





Two Part Pourable Silicone Pumpkin Mold

December 1, 2016

For this project, we will use pourable silicone to create a two part mold of a pumpkin. Two part silicone mold requires two separate pours of silicone, so these types of molds usually take two or three days to make.

Materials needed:

  • Small pumpkin
  • AeroMarine 128 Pourable Silicone with Catalyst
  • Non-sulfur, non-drying modeling clay (Plasticine, Plastalina)
  • Cardboard (or foam board)
  • Hot glue gun
  • X-Acto knife
  • mixing cups and mixing utensils
  • Scale that weighs grams
  • Small plastic straw, swizzle stick or plastic toothpick (to vent the stem of the pumpkin)
  • Silicone-to-Silicone mold release
  • Gloves
  • Sharpie pen

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • First, we need to construct a mold box to fit the pumpkin from cardboard and hot glue. I measure and cut the cardboard for the sides and bottom of the box first, but don’t glue them together yet.


  • Next, we need to embed half the pumpkin in modeling clay. The clay acts as a place holder for the second half of the mold. I like to clay the piece in before I glue the sides on the mold box, I find it easier than trying to work the clay into the already constructed box.


  • Then, use the hot glue gun to glue the sides of the box into place. Next, I apply a seam of hot glue to the outside of the box where the cardboard pieces meet. This ensures that the box is tightly sealed, with no place for silicone to leak out. I then use a small amount of clay to seal any gaps between the mold box and the clay.
  • Because of the curve of the pumpkin’s stem, I’m worried that an air bubble will form at the tip of the stem when it is time to cast the piece. So I’m going to press a plastic toothpick into the clay from the tip of the stem to the edge of the mold box.
  • We also need to create registration marks, or keys, in the clay.  These indentations and matching protrusions will help the two sides of the mold lock together correctly, so when I cast the piece there isn’t a lot of flash, which is casting material leaking between the two sides of the mold. I use the end of a sharpie pen to make indentations in the clay, as you can see in the picture. You can also see the toothpick embedded in the clay as well.


  • Now that the mold box is ready, we need to weigh out and mix the silicone. The 128 Silicone is a tin catalyzed, condensation cure silicone that is mixed 10:1 with the pourable purple catalyst. For the first pour of this mold, I put the empty mixing container on the scale and zeroed the scale out. This is so I’m only weighing the silicone, not the plastic mixing container. I weighed out approximately 2600 grams of silicone and 260 grams of catalyst. As you can see in the following picture, the catalyst is quiet a bit thinner than the silicone. Just mix carefully and slowly, taking care to scrape the sides and bottom of the mixing container, until it is one uniform color.


  • When I pour the silicone into the mold box, I pick a corner away from the piece and pour the silicone “high and thin”, that is, I hold the container a foot and half above the mold box (high) and pour slowly so the silicone comes out in a thin ribbon (thin). This helps reduce air bubbles in the silicone and lets it flow slowly around the piece, which further prevents any air bubbles.

img_20161117_102317 img_20161117_102331

  • Once the silicone is all poured, I lift the mold box about an inch or two of my work table and drop it several times. I do this for a few minutes. This helps encourage any bubbles to rise to the surface of the silicone and pop.
  • This silicone takes 16-24 hours for a full cure, so I’ll come back the following day to finish the second half.


  • After the first pour is cured, I rip apart my carefully constructed mold box, taking care to keep the pumpkin embedded in the silicone.


  • Next, I pull all the clay off the pumpkin. Make sure you don’t pull the plastic toothpick out because it needs to stay in the silicone like the pumpkin.
  • I use another toothpick to clean off any little bits left behind after I remove the bulk of the clay.

img_20161117_091151 img_20161117_092036

  • Then I cut more cardboard to make another mold box to fit around our first half of the mold. Before I glue to mold box in place, I generously spray the mold release on all sides of the first half of the mold. That way if any silicone leaks down between the box and the first pour, it won’t bond and make my parting seam hard to find.
  • Once the box is constructed, I spray more mold release on the first half of the mold. I focus on making sure the silicone, not the pumpkin, is well coated with the release. Some will get on the pumpkin and that’s fine, but the important thing is to make sure the silicone has a good, thick coat of mold release. I’m using Petrolease, which we carry, but you can also use plain, old Vaseline.


  • Now I weigh and mix more silicone, this time approximately 1800 grams of silicone and 180 grams of catalyst because this side is slightly smaller than the other. I pour high and thin into a corner, pick up and drop the mold box for a few minutes and leave it to cure until the following day.
  • The second pour is cured.  Again, I tear apart the carefully constructed mold box. You can see in the next photo where some of the second pour leaked down between the first half and the box, but because of the mold release, it pulls way easily and can be trimmed away.


  • After trimming the excess silicone, I can see the parting line and easily pull the two halves apart. Next, I can remove the pumpkin and the tooth pick to see the finished mold. Sometimes little flecks of clay can be left behind on the mold. The best way to clean a silicone mold is with warm water and dish soap. Do not use and abrasive soap or an abrasive sponge because you don’t want to scratch the mold.


That’s it!  Here is a lovely two part mold of a pumpkin. From here, you could use a urethane casting resin to cast a pumpkin and paint or decorate it anyway that you wish.



Happy Thanksgiving!

November 22, 2016

Happy Thanksgiving! Our blog will be back next week with a post on making a two part block mold of a pumpkin.


Different Types of Common Molds.

November 4, 2016

This is a brief overview of the different types of molds you can make with silicone, latex and urethane. This list is by no means complete. Rather, it consists of pictures and a short description of the more common mold types. If you have questions about a particular project, you can always give us a call, toll-free, at AeroMarine Products 877-342-8860.

Types of Silicone Molds:

Pourable silicone makes block molds. Block molds are created by putting an original in a container and pouring the silicone around the piece. They can be one piece or multiple pieces. They can also be a multi part mold, meaning one mold that has multiple cavities for casting.

  • One piece block mold


These purple molds are basic one part, one piece block molds. For the mold on the right the original (a clay witch’s hat) was anchored to the the bottom of a square box and the silicone poured around it. For the mold on the left (a bat), I made a custom mold box from cardboard and hot glue. Because of the bat’s unique shape, I didn’t want to waste a lot of silicone by putting the original in a square shaped container. The silicone only needs to be a half inch to an inch all around the piece.

  • Multi part one piece block mold


These multi-part one piece block molds are made the same way as the previous block mold. The difference is that it has two (or more) original pieces anchored in the mold box.

  • Two part block mold


To create these types of molds, you encase half your original part in a sulfur-free clay inside the mold box. For the mold on the right (rubber duck), you can see the vents at the tip of the duck’s bill. These vents prevent air bubbles from forming in those areas. On the mold on the left (an apple), you can see the sprue for pouring in the casting material. Both molds make use of registration or key marks to help the sides of the mold fit together tightly.

Here’s an example of a mold box with the original piece half encased in clay:


The straw on the bottom right will become the sprue, the other plastic sticks will become vents to prevent air bubbles.

  • Two part “squish” block mold


Squish molds are called that because once they are made, you pour a small amount of the casting material into the cavity part of the mold and then place the convex part of the mold on top, essentially squishing the casting material into shape. These molds can be a bit messy until you figure out how much casting material is needed for each cast.

  • Multi part block mold

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This is a four part block mold of a coffee mug. The bottom image is the mold fully assembled. This was made by encasing 3/4 of the piece in clay pouring silicone, allowing it to cure and then removing the piece from the mold box and clearing another bit of clay off, poring the next area of silicone and so on until I had a four part mold. I will be doing a how-to blog post in the near future on two part and multi part block molds that will have a lot more detail on this process.

  • Glove mold 

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This is the brushable silicone glove mold with plaster mother mold that I made for a previous post. The silicone is brushed on the original piece, usually in 2-3 coats, to create a thin, flexible mold that can be easily pulled off the piece. The mother mold supports the mold while casting. These types of molds are used for pieces that would use a large amount of silicone if done in a block mold, or pieces that are shaped in such a way that making block molds would be difficult. Glove molds are also used when the original is attached to a wall or something and can’t be removed, like decorative trimming or a part of a large facade.

Latex Molds: 

Latex is used when the casting material is concrete or plaster or a type of mock stone material. The reason for this is the latex is much more abrasion resistant than silicone and can stand repeated castings or rough, course material. The latex we carry is only brushable, not pourable.

  • Brushable latex mold with plaster mother mold
  • Brushable latex mold with black rubber powder and gauze


The latex is applied by brushing a thin coat on the original, letting to dry fully and then applying the next coat. You need about 20-25 coats of latex of a strong mold. The mold on the right (tall can) and the bottom picture is made with 25 coats of plain latex and supported with a plaster mother mold. The mold on the left ( a rock) is made with 4 coats of plain latex (the detail or print coats) and then 12 coats of latex mixed 50/50 with black rubber powder, followed by two coats with gauze embedded in the latex. The black rubber powder and gauze make the mold strong and stable enough to not need a mother mold, but they do reduce significantly the ability of the latex to stretch.

Urethane Molds

  • Pourable urethane rubber block mold


Urethane Rubber is used for casting concrete and plaster and other mock stone materials. Like latex, it has a high abrasion resistance and holds up well to repeated castings of rough material. Unlike latex, it is pourable and can be used with pieces where having a poured block mold is desirable. It doesn’t have as much give as silicone because its durometer/shore hardness (75A) is similar to a car tire.

  • Urethane casting resin rigid one part block mold


Urethane casting resin is usually used for casting parts, not for making the mold. However, sometimes the part needs to be soft or made of silicone. In that case, you might make your mold out of casting resin. The general rule of mold making is when casting a rigid part, use a soft mold and when casting a soft part, use a rigid mold. I made this mold (a clay heart) so I could cast the part in silicone.

These are some of the basic common mold types frequently used in molding and casting. We will be posting how-to blogs on all of these mold types and many other projects as well!

Glossary of Basic Molding and Casting

October 27, 2016

If you are new to molding making, the terms can be confusing. I’ve compiled this basic glossary of commonly used molding and casting terms and definitions. This is by no means ALL the molding making terminology, but a helpful list of the most common terms. If you have questions about molding and casting, terminology or otherwise, you can always give us a call, toll-free, at AeroMarine Products, 877-342-8860. We’re here Monday through Friday 9am to 4pm Pacific time, and we’re always happy to answer questions.

  • Air vent – A thin outlet, generally designed as part of the mold, but can also be later, to prevent pockets of trapped air.
  • Ambient – Relating to your immediate surroundings.  Used to refer to the ambient temperature or ambient humidity.
  • Block mold – A mold in a ‘block” shape. The molding material is poured around an original part which is anchored inside a box.
  • Cast/part – the end result of pouring resin into your mold. The copy of the original piece.
  • Cure inhibition – Failure of a material to cure properly. Generally this is caused by contamination, like using a sulfur containing clay with a tin-based catalyst silicone.
  • Cure time – The amount of time it takes a material to cure or harden to usefulness.
  • De-mold time – The amount of time it takes for the mold to be cured enough to be removed from the mold box or the amount of time it takes the resin in the mold to cure enough to be removed from the mold.
  • Degassing – To remove gas, in this case air bubbles, from a material. In mold making, this is achieved by using a vacuum chamber.
  • Durometer/Shore Hardness – The resistance of a cured material to indentation. Most commonly measured on the Shore Scale. Shore A materials are considered flexible and Shore D materials are considered rigid. The higher the number, the harder the material is. For instance, Shore A 10 silicone rubber is similar to a gummy bear, while Shore A 40 silicone is more like a pencil eraser. Shore D casting resin is like a hard hat.
  • Elongation – Recorded at the moment a product breaks from being pulled apart. It is usually stated as a percentage.
  • Flash – Excess casting material that runs over the opening of a mold or any excess casting material that seeps between where two parts of a mold meet. The flash can easily be trimmed away after the casting material has cured.
  • Glove mold – A mold that is brushed on to the original part, creating a thinner, floppy mold that can easily be pulled of the part. Because it is floppy, it needs extra support, usually from a mother mold, when casting. A glove mold can be made from brushable silicone or brushable latex.
  • Mold – The negative form made to reproduce objects.
  • Mold box – A container, not necessarily a square box shape, the holds an original for silicone or other molding material to be poured around it.
  • Mold release – a substance used to release one material from another. Some mold releases are particular to the material being released, like urethane mold release. Others are more general, like using petroleum jelly as a silicone to silicone mold release and also in a silicone mold to release the part being cast.
  • Mother mold – A rigid outer backing made to support a glove mold. Plaster and fiberglass are common mother mold materials.
  • Original/piece or part – The object that you are creating a mold of in order to reproduce it.
  • Parting line – The place where two halves of a mold meet. Parting lines are picked to facilitate easy removal of a part from a mold, usually where an undercut is located.
  • Pot life – The amount of time it takes for a material to double it’s viscosity.
  • Registration marks- Also called keys, these are indentations made in one side of a two part mold. When the other other side of the mold is poured, the mold material will flow into these indentations, creating a sort of placement lock that ensures the two parts of the mold will be held together properly for casting.
  • Room Temperature Vulcanization (RTV) – A two part rubber that requires no special treatment to cure, other than mixing the components together.
  • Rotational casting – A casting process that requires the mold to be constantly rotated while the casting material cures. It results in a hollow cast piece. Also called roto casting, spin casting, and slush casting.
  • SDS – Safety Data Sheet, information on the ingredients of a material, what it is used for, how to store it, how to handle spills and disposal, what safety equipment and first aid is needed when working with the material and other information about the material.
  • Sealant/Sealing agent – A material that is used to coat your original piece/part so that the mold making material does not come into contact with a material in may bond to or may inhibit curing.
  • Shrinkage – The change in dimension between the liquid product used and the finished cured piece/part.
  • Sprue – A funnel shaped opening in the mold where the casting material is poured. Any excess resin that cures in that area is also called a sprue and can be trimmed off after curing.
  • Tear strength/Tear resistance- A materials resistance to tearing. Usually expressed in pounds per inch.
  • TDS – Technical Data Sheet, the information sheet(s) that comes with a product/material. It contains mix ratios, cure time, pot life and other important information you should read before using the product/material.
  • Tensile strength – The force, measured in pounds per square inch, needed to stretch a material before it breaks.
  • Undercut – Any over hang, protrusion or indentation on a part/piece.
  • Viscosity – The measure of an uncured materials resistance to flow, measured in centipoise. Water’s centipoise is 1. The higher the viscosity, the thicker the substance.
  • Work life – The amount of time before the product becomes too difficult to work with. Used interchangeably with pot life, even though work life doesn’t have a defined value of viscosity.

Cold Cast Bronze Skull with Urethane Casting Resin into a Glove Mold with Mother Mold

October 19, 2016

In the last couple of post we covered making a brushable silicone glove mold with a rigid plaster mother mold. Now that we’ve created the mold, we can cast a piece. For the skull mold I’m going to show you how to use bronze powder, urethane casting resin and brown urethane colorant to create cold cast bronze piece, that is a skull that is made or urethane resin that looks like it is made of bronze.

Materials needed

  • Glove mold and mother mold
  • Urethane casting resin
  • Brown urethane colorant
  • Bronze powder
  • Urethane mold release
  • Plastic measuring and mixing cups and plastic mixing utensils
  • A plastic spoon
  • Tape and clips (to hold the mother mold together)
  • Steel wool (I used Course #1, but finer is better)
  • disposable gloves

Your work area

  • Clean, level work surface, covered in paper or plastic for easier clean-up
  • All materials comfortably within reach

Project steps

  • Tape the edges of the mother mold together


  • Once the edges are all taped together, place the binder clips over the tape to further secure the mother mold. Fold the silver part of the clips so they are resting against the mother mold, not sticking straight up.

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  • Balance the mold on some upside down mixing containers, cups or any thing else that will hold and stabilize the mold while casting.


  • Apply a light coating of urethane mold release to the inside of the mold. This will not only help the casting release from the mold easily, it will also help the bronze powder stick to the mold.


  • Pour the bronze powder into the mold. Pour in more than you think you will need to coat the mold. Then pick the mold up and roll it around to coat the inside with the bronze powder. You may need to place your hand over the opening of the mold to ensure that the powder gets all over the interior of the mold.

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  • Pour any excess bronze powder back into the bronze powder container.
  • Place mold back onto cups/containers
  • Measure out equal parts, by volume, of the urethane casting resin. So for this piece we did approximately 12 fluid ounces of the “A” side and 12 fluid ounces of the “B” side. Urethane is moisture sensitive before it is cured, so you don’t want to use it on a rainy day or a day when the humidity is over 50%. Because wood and paper products can also contain moisture, that’s why we use plastic containers and utensils for mixing and measuring urethanes.

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  • Add the brown urethane colorant to the “B” side and mix thoroughly. The purpose of the colorant is to match the color of the bronze powder. This way, if the powder missed a spot or we rub too hard with the steel wool, there won’t be an obvious white spot showing through. Instead it will blend into the color rest of the piece.
  • Mix the “A” and “B” sides together, taking care scrape the sides and bottom of the mixing container. Mix vigorously for about 90 seconds.
  •  Grab the plastic spoon and position it over the mold opening upside down, that is with the rounded (convex) side facing up.
  • Carefully and slowly pour the casting resin over the backside of the spoon. This will break up the pour, so to speak, avoiding a heavy direct pour that could disrupt the coating of bronze powder. Pour the urethane casting resin to the top of the mold.


  • This resin has a demold time of 30 minutes. However it is still pliable when when removed from the mold at 30 minutes. Since I will be polishing the piece with steel wool, I let this piece sit in the mold over night so it will be fully cured and hard when I pull it from the mold.
  • When it is time to demold remove the clips and tape and the mother mold. Grab the mold by the base and pull upward carefully and slowly to remove it from the piece. Don’t worry if this pulls the mold inside out, it will pop back into shape when you turn it right side out.


  • Now we have a lovely brown skull!
  • To bring out the shine of the bronze powder, rub with the steel wool, in a circular pattern, not too hard. I used a course #1, but i usually prefer finer steel wool. The course is just what I had in the shop. You want to rub firmly, to bring out the shine, but not so hard as to completely rub the layer of bronze powder off.
  • Now we have a skull that looks to be made of bronze, when in fact it is a lighter weight urethane resin.

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That’s the cold cast bronze process using urethane casting resin. There are other types of metal powders available, but the process is the same for using them.Next post we’ll be doing a two part pourable silicone block mold of a pumpkin.


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