Introduction: Casting and Mold Making for Edible Foods
Have you seen food molds and wanted to make your own chocolates, ice cube trays or other edible items? I did and recently took a few classes at 757 Makerspace in Norfolk, Virginia USA to learn about molds, casting, vacuum forming and working with food. This instructable will walk you through the steps needed to make your own small food molds that can be used for presents, edibles or just a unique gift for that special person in your life. It is also a great way to surprise kids with ice cubes of their own face or favorite character on a warm day.
Step 1: What You Want to Make
To get started you need to have the item that you want to make a mold of. For this step you can take something you already have. You can 3d print, carve, or make it using the process you are most comfortable with. In the images, you can see the gear "logo" of 757 Makerspace (gear with an M inside of it). To make this shape, I used the ShopBot Desktop CNC with 1/4" Baltic Birch wood. My goal was to make a few single gear individuals molds and a large mold with 16 gears total to make a plate of chocolates quickly.
Step 2: Need More Copies Quickly
This is an optional step if you need more "duplicates" of your part quickly as apposed to hand something each time. I needed 16 of the wood gears from the previous step. I used a small vacuum former and a thin sheet of styrene plastic (also called Polystyrene). You can find out more about this here. There are some great instructables on using and making your own vacuum former. Summary: the vacuum former heats up the plastic with the gear placed on the tray. When you turn the vacuum on, the heated plastic will form around the part (gear). If you look at the image, we cut the formed plastic into individual small pieces to handle easily. To duplicate many of the gears quickly we used a material from SmoothOn called Smooth-Cast 300. It is mixed according to the directions (1:1 mix of part A and part B). It starts out clear when mixed. Cure time for this is 10 minutes in the cast and turns an opaque white when it is ready. Now we have copies of the parts we want to mold quickly.
Step 3: Prep the Mold
With our part(s) ready to make a mold, we need to make a "container" that is liquid tight that we can pour into. There are many ways to do this and in the images you will notice a few, such as: Clay, Cups, Plastic, Wood, Lego Blocks and a new favorite is Corrugated Plastic (shown in the images). In the Corrugated Plastic example we used a base and walls for the sides that are hot glued into place and painters tape on the outside to hold the sides together. Make sure your "walls" and the "base" they are connected to are watertight as the material we mix in the next step starts as a liquid and will leak through if it is not watertight.
Step 4: Food Grade Silicone
If you are going to be making edible foods you must use a food grade silicone. We used a material from SmoothOn called Dragon Skin. This particular silicone is food grade quality and is very strong (meaning you can push, pull, bend, etc. the final product and it will not tear and will return to its original form without distortion). Dragon Skin is mixed at a 1:1 ratio. My recomendation is to always mix a little more than you think you need. One downside to the Dragon Skin is that both part A and part B are clear, so you will need to mix thoroughly. An alternative material is Smooth-Sil 940.
Step 5: Time to Pour
Your Mold Box is prepped and watertight and the silicone material is mixed. You are ready to pour... slowly. You want to pour enough to cover the item you are casting from + a bit more for strength. Tip: if you hold your pouring container up higher, this will remove a large portion of air bubbles that may have been introduced during the mixing process. Set your box in a flat location where it will not be disturbed for several hours as it dries. Depending on the temperature and humidity in your area, this can be anywhere from 5-10 hours. When I made the gears, the room was a consistent 65 degrees and 20% humidity and our larger mold of 16 gears sat for 12 hours. Read the directions and if it is tacky still to the touch, give it another hour or two to firm up.
Step 6: Removal
With your silicone cured, you need to remove this from the "box" you made. In our example, we removed the corrugated plastic by taking off the painters tape, then pulling it apart from the hot glue on the base. What we were left with is the food mold. It is thick enough that it holds its shape (see the side picture) and deep enough that we can pour chocolate or other material into it.
Step 7: Making Chocolate or Other Foods
You can read up on the food material of your choice. For the gears, we wanted two style of chocolates (one just chocolate, the other with coconut and hazelnut with the chocolate). Tip: we found that chocolate from the baking section of the grocery store with a decent fat content melts and pours well. We went with 60% cocoa dark chocolate for one batch (any higher and it does not seem to separate when heated) and semi-sweet chocolate. We did not have a double broiler to melt the chocolate but found that using a pyrex measuring bowl filled half-way with chocolate chunks worked well. We microwaved it on 50% power and for 30 seconds, then stirred for 15 seconds and repeated until it was mixed thoroughly in an almost liquid state ie pourable. We did this about 4-5 times before we poured. Your microwave may vary (start slow). To make this harden faster, we put it into our freezer. After 10 minutes, it was easy to pop out because of the flexible mold. The mold is very flexible, push/pull as needed to remove your chocolate or material of choice, then serve. Clean the excess bits off the mold to use again. After this, we repeated the same process using Lego Men and now have chocolates and ice cubes that are a hit with kids and adults!