Making Silicone Molds without Air Bubbles

One of the most common methods for chocolatiers to make their own molds is to use food grade, liquid silicone rubber.  The problem is that liquid silicone rubber is very expensive and can take a long time to set.  If your silicone inadvertently gets air in it while mixing or pouring, you may very well go through the whole process only to find that your mold did not turn out right because of one unsightly placed air bubble.

There are several things that can be done.  The simplest form is not over-mixing and brushing a small layer of the silicone on the model before pouring the whole mold.  This way you get into the detail and have less air bubbles on the surface where it matters most.  The next best thing you can do is use a vacuum degasser.  To use a vacuum degasser, the mixed liquid silicone is put in a chamber before it is poured.  This process will break up most of the air bubbles before casting.  This is very effective, but not all the way as air can be brought back during the pouring.

The best way to ensure a bubble free mold is to use a pressure casting method.  A pressure pot is a metal chamber that uses a compressor to cure the mold under pressure.  The liquid silicone is poured over the model then placed in the chamber.  The pressure, max 60 psi, eliminates the bubbles during the cure process.  You can buy pressure pots at Smoot On, or I have seen them used for the paint industry which can be bought at many places, even Amazon (link will take you right to the pressure pots).

Word of caution:  do not attempt to make your own pressure pot as they can explode.

To read more about mold making see our in depth instructions on The Chocolate Mold Factory's Main Site under "Personalized Molds".  There are tutorials about designing molds and how to make them.  Though the site is geared towards chocolate molds, these instructions are the same as would be for any other type of non food grade mold.

How Much do Custom Chocolate Molds Cost?

The cost of a custom chocolate mold greatly depends on the design and mold material.  For example, the least expensive type of custom chocolate mold is going to be a simple logo put on a bar of chocolate.  The price will start at around $150, though it varies greatly.  Most will charge around $300 for this type of mold.  The type of mold you will receive for this price is a thin plastic vacuum formed hobby mold that is good for short term use. 

Many people want a professional style chocolate mold, hard polycarbonate.  No doubt polycarbonate chocolate molds produce the best results and last the longest.  However, these molds are made by injection molding and the price is in the thousands.  Unless you are having these made for long term, high volume production, you simply cannot justify the cost.

The middle of the road is a silicone chocolate mold, or there are other food grade epoxies that can be cast.  These molds will start around $400 and are a good option for getting a higher quality mold, yet not going full blown into an injection mold. 

Generally the time to make a mold takes 3 weeks or more.  The design process takes the longest in order to make sure the chocolate de-molds properly and that the artwork is satisfying to the customer.

Can you Make Chocolate Molds with a 3d Printer?

I have spent a lot of time researching 3d printers for a solution to make chocolate molds.  A 3d printer would be ideal as you do not have to know how to use CAM software or generate toolpaths as you do with CNC machine.  Just design in 3d modeling software and print.

To date, I am yet to find an acceptable 3d printing solution that is affordable.  There are certain machines that are capable of very high quality fine printing, but they cost over $150,000.  The lower priced machines are good for making larger models with larger text.

First, most 3d printers use only certain types of materials that are not food grade.  It may be the type of plastics that are used or the adhesive functions used to build the layers that are not certified for contact with food.  So, while it may be fine for your individual use or display purposes, this would not be acceptable for use in food or molds you are selling.

Second, 3d printers are best suited for larger items and cannot get the best detail for text in a small format.  I once tested this on a Dimension 3d printer which makes parts by basically melting a thin plastic rod (looks like the weed whacker spool) and then depositing it.  I wanted to make a standard size bonbon with small text on it.  While it was fine to make to the base of the chocolate, the text did not come out.  It was just a blob of illegible melted plastic.  I did see the ZCorp 3d printer produce small text.  But the ZCorp machine uses non-food grade materials and has a very rough surface.  That process is of depositing a thin layer of a plaster or starch type substance, then adhering between layers.

Third, the surface finish on a 3d printed part is still quit rough no matter which you are looking at, unless you get into these very expensive printers.  Even with sanding, it's not going to have a good enough surface to produce a smooth chocolate.  Chocolate will pick up very fine detail in a mold.  It will not have the proper luster.

That being said, I know they are making huge advancements in the 3d printing world daily and I continue to seek for a solution. 

Vacuum Degassing Silicone Chocolate Molds

Food grade silicone chocolate molds are very expensive to make and they take alot of time to set up, so it is really important to try to get it right the first time. One of the major hurdles in making liquid silicone molds is to minimize air bubbles. One air bubble can ruin an entire mold. Air bubbles are the result of the mixing and pouring processes.

When mixing a silicones, it is very important to follow the manufacturer's directions as closely as possible. Do not stir the mold making materials quickly or in a random pattern. The best way is to move your mixing stick in a slow, figure 8 pattern. Then when pouring, first brush the silicone onto the face or details of the mold. Then pour the remaining materials slowly and over your mixing stick. This will help to break up many air bubbles.

A more precise and professional way to accomplish this is through the use of a degassing chamber, like the one below. To use a degassing chamber, you will first mix the materials and then put it in the chamber, which is connected to a vacuum source. This will pull out all the air bubbles before you pour the silicone and your mold will have a better finish.

Vacuum Chamber and Plate

(Click title for more info)

I am a big fan of the mold making videos provided on the Freeman Supply webpage. Here is a great demonstration they made on using a vacuum degassing chamber.

Silicone Plastique / Culinart

I often receive emails from people looking for some odd shaped mold. Most people assume that you have to pay a fortune for a custom vacuum formed plastic chocolate mold. However, there is a much simpiler and cost effective method.

I highly recommend going to the newly designed MakeYourOwnMolds.com website to look at their silicone moldmaking products. MakeYourOwnMolds.com is a part of Culinart. Amongst their product line up is Silicone Plastique, which is a putty food grade silicone; Silicone Spread, which is a thixotropic food grade silicone that is thick and spreadable; and CopyFlex which is a liquid food grade silicone. They also sell supporting supplies such as sealants and release agents. We will just talk about the Silicone Plastique for now since it is the easiest and cleanest to use.

One example of a common inquiry is a letter in a certain font. If you look at the stock plastic chocolate molds for sale, you will see that there aren't many choices. So, I try to tell people to go to a hobby store and find the letter that you want as a model to make a mold from. This can be made out of wood, clay, or even fabric. It just needs to have some degree of thickness to it.

The model must first be prepped before the Silicone Plastique can be used. Usually this will involve adhering the item to a board using kneading clay. Make sure whatever you are using is FDA approved, or at least non-toxic. The item must also be sealed so that the mold making material doesn't penetrate the surface of the model. Depending on the item you may want to also use a release agent so the silicone does not stick to the model. Again, since you will be using this in the preparation of food, you want an FDA compliant material. These products can all be obtained from the folks at Culinart.

Once the model is ready, you will mix the two parts of the putty together to activate the mold making chemicals. You must work fairly quickly before the materials begin to harden. According to a video on their website, you have about 10 minutes to make your mold once you have mixed the two parts together. If your mold is large, you may want to mix the putty in steps so you can take your time. At any rate, now that the putty is mixed you will want to apply it to your model. It is important to lay the silicone on the model in a manner that does not trap air. After you have applied the materials, it will take approximately an hour to cure, or completely harden. You will need to thouroughly wash and dry the mold prior to use.

I highly recommend that you go http://www.makeyourownmolds.com/ and watch the lace mold making video. It is an excellent demonstration with very good tips that you can use when making any mold.

New Vacuum Forming Machines

Now you can buy vacuum forming machines through Amazon.com. There are two sizes available: 12" x 12" and 12" x 18". Below are pictures/links to the machines.

The item description for the machine is: Our Table Top Vacuum Former is perfect for small businesses and hobbyists who want to create parts in plastic up to 1/8" thick. Produce intricate shapes with results that rival expensive commercial machines in their incredible accuracy and detail: prototypes, custom packaging, RC car bodies, model rocket nose cones, molds for plaster or concrete, chocolate and candy, candles, and soap making. Our 12"x12" Vacuum former includes a perforated aluminum vacuum platen (the top surface that delivers the vacuum under the hot plastic) that is computer designed and precision CNC machined to maximize air flow and eliminate unnecessary volume - both critical to rapid air evacuation and professional vacuum forming results. Detailed, step-by-step instructions along with sources for vacuum formable plastics are included. Compatible with all types of thermoform plastic: ABS, Acrylic (Plexiglas), Butyrate, PET-G, Polycarbonate (Lexan), Polyethylene, PVC, Styrene, Vinyl, etc. Requires house hold oven and Shop-Vac style vacuum cleaner with 1 1/4" hose/adapter.

Vacuum Forming Explained in 3 Easy Steps: Step #1: Secure your plastic between the vacuum former's metal frames. Attach your Shop-Vac (not included) to the vacuum former. Place your model on top of the perforated aluminum vacuum platen. Step #2: Place the plastic in your kitchen oven and watch as it becomes soft and begins to sag. Align the metal frames with the vacuum former's guides and lower the plastic over your model. Step #3: The hot plastic forms an air tight seal around the vacuum platen's edges. Vacuum pressure pulls the hot plastic down around the model. After cooling for a few seconds the plastic part is complete.

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  Make your own prototypes, custom packaging, RC car bodies, or model rocket nose cones
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  Create custom molds for plaster or concrete, chocolate and candy, candles, and soap making
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  Forms Plastic Sheets 12" x 12" Up to 1/8" Thick (9 3/4" x 9 3/4" Usable Area)
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  Includeds detailed, step-by-step instructions along with sources for vacuum formable plastics
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  Requires house hold oven and Shop-Vac style vacuum cleaner with 1 1/4" hose/adapter

I think this looks like a higher quality hobby vacuum forming machine than some of the others sold on the market. The box looks to be well made and I particulary like that the platen area is metal. This results in better forming as it will transduce heat better. As for the price, it is very competitive. Other companies that sell inferior products also make you buy plastic with the machine at a very high price. You can buy plastic through many sources on the Internet, such as U.S. Plastics, much cheaper. I recommend using PETG (Vivak) for making chocolate molds.

See The Chocolate Mold Factory.com main pages for more instructions on how to use a vacuum forming machine like this.

Making Chocolate Molds with Silicone Putty

Townsend Atelier Knead-A-Mold

If you want to mold an object to replicate it in chocolate, one method is to use a silicone putty. Silicone putties carry the same characteristics of liquid silicone, but can be used without the mess and the long wait time. Generally the putty will come in two parts: the actual silicone and a curing agent. Curing agents are used to harden or set the material and can be tin-based or platinum-based. For the most part, platinum-cured silicones are preferred; however, it is usually more expensive than their tin-based counterparts.

If you are going to be using the silicone to make a chocolate or other food mold, you must ensure that you are buying a food grade silicone. There are many companies that sell regular grade silicones, but this is not food grade. So, just be careful. Some sources that I know of for food grade silicone in a putty form are Townsend Atelier Knead-A-Mold, Sugarcraft, Culinart Silicone Plastique, and Dick Blick. Prices for the lowest quantity available at each are:

Knead-A-Mold: 6 oz. for $15.00
Sugarcraft: 1 lb. for $25.95
Silicone Plastique: 6 oz. for $12.00
Dick Blick: 8 oz. for $15.99

All of the above dealers sell larger quantities, but I thought I would list the minimum because my experience is that most people prefer to spend the least amount to a try a product out. Obviously, the larger quantity you buy, the cost per ounce decreases.  You should do a similiar price per ounce comparison that considers shipping costs before deciding to buy from a particular place.

To use the silicone putty, you simply knead the two parts together and press the object into the putty. After it has cured for the proper time, remove the object and you will have a flexible silicone mold. For a great pictorial of this process, I highly recommend the Culinart Silicone Plastique page or the Townsend Atelier Knead-A-Mold page.

The Knead-A-Mold product was recently featured on Martha Stewart Living: Good Things ‘The Art of Cakes II’  which orginally airred on December 16, 2008 on The Style Network. Check for repeats at http://www.mystyle.com/.