Making Chocolate Molds Out of Silicone Putty by TechShop

Making Chocolate Molds out of Silicone Putty by TechShop
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You will need:
1) Chocolate chips
2) Hotplate or stove
3) Double-boiler or two pots that nest
4) Spoons
5) Equinox putty (more on this in the next step)
6) Something from which to make a mold -- this is called a "master"

Optional tools and things that make it easier:
1) Wax paper to place under your mold to keep it from sticking to the table
2) Paint brush you can use with food
3) Rolling pin for large and sheet molds

Step 1: Prepare the Silicon

Working with Smooth On's Equinox putty can be deceptively challenging.

A breif introduction to Equinox putty.

Equinox putty is a two-part RTV silicone rubber compound that is food safe.  Please read here.  Two-part means there is a part A and a part B that must be mixed together to begin the curing process.  RTV stands for room-temperature vulcanization which means that it will do all this at standard pressure and temperatures.  This stuff is very handy for making quick simple molds and is an excellent way to make a depression mold or imprint.  It is limited, however, in that it can only pick up the level of detail offered by, say, play doh which has a nearly identical consistency.  It is also not very good at full 3d shapes.  More on this later.

We're using the Equinox #38, which has two main properties which make it appealing for what we want to do today.  First, it has a pot life of 4 minutes.  This refers to the time you have from when you start mixing the two parts until it becomes too hard.  Second, it has a demold time of 30 minutes, which means you will be ready to peel back your master from the mold in a mere half-hour.  Smooth-On does make other versions, but this is the most useful in my opinion--check them out here.

STEP 1:

Before we jump in, make sure to start by mixing the purple part B (blue label) putty by itself.  You can do this by kneading it in your hands.  You want to have about as much as your master (the thing you want to make a mold of) in volume.

Step 2: Make the Mold

Once your part B is thoroghly stirred, take about as much of part A as part B.  Equinox 38 has a 1:1 A to B ratio--equal parts.  Make sure to clean the surface you are working on or lay down some wax paper.  It is important to get an idea of what you want to do before you start mixing the parts because once they touch you have a 4 minute pot life.  It's closer to 2 minutes before it becomes really difficult to work.  Try to have your object embedded in about 1 minute 30 seconds.  This stuff, like Play-Doh works best on things that "smoosh" into it.  Rather than try to make a full 3D object, think of something you can imprint in it.  This is where a rolling pin comes in nice if you want a whole sheet of something or a large flat object.  Today we're going to use a tiny sea turtle from the dollar store so that won't be necessary.

When you are ready:  knead A and B together as fast as possible.  Keep an eye on the clock.  Once your mixture is uniform (no to few white streaks) quickly set it down and mash your master into it.  If two minutes pass before it is thoroughly mixed, just go for it...time is up.

You are done.  Wait 30 minutes for the mold to cure.  Don't move your part until then.  In the mean time, lets get the chocolate going.

Step 3: Melt and Pour the Chocolate

Using a double boiler, or two pots that nest, to melt the chocolate is quite easy.  Fill the bottom pot with water.  Set on medium heat and put the chocolate chips in the top pot.  Take care to not let any water get into the chocolate pot.  Water and chocolate don't mix.  Also take care not to let the chocolate get too hot.  If the water begins to boil, you're approaching "too hot" conditions.  Its best to heat slowly so that when the chocolate chips melt you can stabilize the heat.  Stir occasionally.

Once it's melted, you can take the master from your finished mold.  (30 minutes after setting).  

IMPORTANT:  Follow the instructions for full "food safe" effect from the earlier link. 

You can now use a spoon or paintbrush to place the chocolate into the mold.  Pour will also work for larger mold.

Place the mold in the freezer for another half hour.  For better results, wait longer--who has the patience for that, right?

Step 4: Demold and Enjoy

Demolding is sometimes very difficult.  As you make more and more molds out of the putty you will realize a few things.  One, small details or thin "twigs" will break.  Chocolate is very brittle.  And two, thin molds are better than thick ones because you can pull the edges away and break the grip on the chocolate.  Also, having a thin bottom allows you to pop the chocolate out from beneath with a push.

This is a good time to talk about a draft angle.  This is the angle at which the walls of your master (if any) meet with the perpendicular from the bottom part of your mold.  Think of it like this:  which would be easier to get out of the mold:  a cube or an upside pyramid?  The pyramid, of course, because it has such a pronounced draft angle.  Try not to mold anything with a 90 degree wall.  A 1 or 2 degree difference makes a huge impact.  Also, a negative draft angle or overhang is nearly impossible to work with.  If you want to make a mold of something like that, you must use either: a two part mold (one that separates) or, with chocolate--this is easy, fuse two or more parts together with a little warm water after they come out of the freezer.  You can make a nice full 3d mold in this way.

Pro tip:  The paintbrush allows you to paint a shell.  I was able to make a star-shaped peanut butter cup with this method.  A layer of chocolate, freeze it, another layer of chocolate, and so forth.  Delish!

Enjoy,
~Zack

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