Introduction: White Chocolate Skulls in PLA Trays

About: Anna Kaziunas France teaches the "How to Make (almost) Anything" rapid prototyping course in digital fabrication at the Fab Academy at AS220. She is also the Dean of Students for the Global Fab Academy program…

Every Halloween I make treats to give away.  This year I had two 3D printers at my disposal, so I decided to make 3D printed chocolate mold maker.   I used food safe silicone to cast the chocolate mold from the 3D printed mold form.  Then I cast many, many chocolates.  

The skull is from a 3D scan I created using 123D Catch.  I used OpenSCAD script to make a mashup of a parametric box by Thingiverse user acker, and my skull to create the mold maker.  I also created trays for the chocolates using the parametric box script. 

The candy trays were printed in PLA, so they would relatively "food safe" at least compared to ABS.  I cast many, many batches of white skull chocolates and then placed them in the PLA trays.  I then placed the trays in treat bags and sealed them with twist ties.  

The OpenSCAD code and STL files are all available on Thingiverse (and at later steps within this Instructable):
The Chocolate Skull Mold Maker
Skull with Pointed Teeth (cleaned and repaired scan)

The scan is available from 123D Catch:
My original skull scan (before cleanup)

Step 1: Bill of Materials

You will need the following items in order to recreate the White Skull Chocolates:

- Access to a 3D printer (I used a MakerBot Replicator) or use of a 3D printing service (like Ponoko or Shapeways)
- PLA filament to print on that printer
- Smooth On SmoothSil 940 food safe silicone rubber
- Chocolate Melts (no tempering required) - I like this brand
- Soy Lecithin (softgels) - I found these at Whole Foods in the supplement isle
- food thermometer, I find that digital ones with big letters are easiest to read.
- double boiler (or a tall soup pot and a small glass mixing bowl)
- sharp knife
- cutting board
- small spatula / spreader

Optional items:
- coco power (I used Green & Blacks)
- Candy maker's cotton gloves (keep your fingers from marring the chocolate when demolding)
- Food safe squeeze bottles or a chocolate funnel (keeps the process from becoming overly messy)
- Bamboo steamer (can be used in place of a double boiler or tall soup pot / glass bowl combo)
- Plastic treat bags with twist ties (I bought mine at Joann's Fabrics)

Step 2: Design Your Own Mold in OpenSCAD (optional)

For those who do not want to design their own mold, you can still play along.  Skip this step and use the provided linked files.

I designed this mold using a mashup of OpenSCAD and a scanned skull.  I don't seem to be able to upload OpenSCAD files here, so I pasted the code below. 

You can also grab the OpenSCAD files, so you don't have to copy and paste.  If you want to play around with the mold code, make sure the vampireSkull_0.2.stl (I was unable to upload the file to instructables) is located in the same directory as the OpenSCAD file. 

You can substitute your own STL for the mold, just change the "filename" variable to the name of your STL.  Make sure your STL is in the same directory or provide a pathname for this to work. 

/* ----------------------------------------------------------------------
Skull with Pointed Teeth Chocolate Mold
Created with a scanned with 123D Catch. The raw scan is available here:
This mold is a work in progress, it is currently only partially parametric. 
Make sure you download the vampireSkull_0.2.stl file and place it in the same folder.
You may want to adjust the wall width to a larger number.  This will print, but it may be porous when you
attempt to pour mold material into it. I used liquid tape on the bottom to make it water tight.  
Anna Kaziunas France
derived from acker's parametric box
which was derived from hippiegunnut's

//skull spacing
filename = "vampireSkull_0.2.stl"; //name of the STL to scale
skullStartXPos = 30;
skullStartYPos = 23;
skullStartZPos = 0.9;
skullXSpacing = 45;
skullYSpacing = 35;

//mould pour box vars
//Replicator max build platform: 225 x 145 x 150 mm
compx = 140;  // Size of compartments, X
compy = 112;  // Size of compartments, Y
wall = 1.3;  // Width of wall ("thin" by default")
nox = 1;   // Number of compartments, X
noy = 1;   // Number of compartments, Y
deep = 35;  // Depth of compartments

union() {
//import that thing! Move it around in rows that are sort of adjusted for the size of the box!
for ( i = [skullStartYPos : skullYSpacing : compy] ) {
  translate ([skullStartXPos,i,skullStartZPos]) import(filename, convexity=30);
  translate ([skullStartXPos+skullXSpacing,i,skullStartZPos]) import(filename, convexity=30);
  translate ([skullStartXPos+skullXSpacing*2,i,skullStartZPos]) import(filename, convexity=30);
//create the mold pour box with acker's parametric box code
difference() {
  //create the outside box, can be multiple compartments if you like
  cube ( size = [nox * (compx + wall) + wall, noy * (compy + wall) + wall, (deep + wall)], center = false);
  for ( ybox = [ 0 : noy - 1]) {
              for( xbox = [ 0 : nox - 1]) {
     translate([ xbox * ( compx + wall ) + wall, ybox * ( compy + wall ) + wall, wall])
     cube ( size = [ compx, compy, deep+1 ]);

Step 3: Print the Mold Maker on a 3D Printer

Print the mold form on a 3D printer.   If you don't have a 3D printer, go to your local hacker / maker space / fab lab and rent some time on theirs.  If you don't have any of those near you. you can always use a 3D printing service like Shapeways or Ponoko.

You can get the mold files on Thingiverse.  Unfortunately, I was unable to upload the STL files for printing in this Instructable, perhaps the file size is too large.

For those following along on their 3D printers at home, I recommend printing the Chocolate Skull Mold Maker with 13% infill and 3 shells.

I have provided two versions of the Chocolate Mold Maker STL file; on with thin walls (1.3mm) and one with thicker walls (2.3mm). The one with thin walls in not completely watertight if you print it with a raft. I used liquid tape on the bottom to make it water tight, but in the end the rubber mold mix was very thick and I don't think the liquid tape was actually necessary. (see step 4 for details)

The thicker on will take much longer to print. In the end, the thin walls one should be fine to pour the silicone rubber into, but I have only made one mold so far.

Step 4: Mix and Pour the SmoothSil 940

Take the Smooth On SmoothSil 940 food safe silicone rubber and mix it according to the proportions on the package.  Pour into 3D printed chocolate mold maker.  Fill mold so that it covers the skulls by about a half inch or close to the top of the mold.

I don't have access to a vacuum degasser (yet), so to help alleviate possible bubbles from forming in the mold I placed on a subwoofer while music with heavy bass was playing.  I also used an electric toothbrush without the brush head attached to vibrate the bottom and sides of the outside of the mold to get bubbles to come to the top. 

I don't know how effective these measure are, but I did not have any problems with bubbles or the mold material loosing detail.

Let the poured mold set for 24 hours and follow heat curing instructions. Read the datasheet.

Note: I covered the bottom of the "thinner walled mold" with black liquid tape (liquid rubber).  You can see it the pictures.  I was worried that the model was not completely watertight, but I don't think it is actually necessary.  The Smooth-Sil 940 was so thick that it wouldn't have leaked out before setting up anyway.

Step 5: Demold

Demold. You will probably have to destroy the 3D printed form completely. I tore mine completely apart.  Some of the skulls have to be removed one by one.  Overall it was pretty easy to demold, once I accepted that I was going to destroy the mold maker.  

Give the mold a wash with soap and water in the sink.  Let it dry completely before attempting to cast chocolate.  Water does bad things to chocolate when you are casting it.

Step 6: Add Slits to the Mold

Cut notches in the mold with a razor blade at the base of the skulls (see the pictures).  This will make it much easier to demold the chocolates.

I came across this by accident.  After demolding many rounds of chocolates, the base of one of the skulls started to split a little from flexing the mold. I found that it had no impact on the quality of the chocolates coming out of the mold and it made it much easier to demold the chocolates. I cut little notches with a razor blade straight back perpendicular to the base of all of the skulls. (see pic, the notches are only visible if I flex the mold) It makes it much easier to get them out of the mold.

Step 7: Extract the Soy Lecithin From the Softgels

The soy Lecithin will help with the demolding and has other benefits when used in molding chocolate.  I used Whole Foods softgels (available in the supplements isle).

I cut the softgels open and squeezed the oil out. I not very precisely used around two small handfuls of chocolate to the oil contained in 4 Lecithin pills. Discard the softgels after squeezing out the oil.

Step 8: Melt Chocolate

Get white chocolate melts that do not require tempering.  I used these and they worked great.  You could use tempered chocolate, but it is not covered here.

Heat chocolate melts in a double boiler.  I followed these detailed instructions. Temperature is  very important.   While the chocolate melts, use thermometer to measure the temperature. Heat to between 100-105° F. Do not overheat!

While melting the chocolate, add a small amount of Lecithin that we obtained in the last step. I used two small handfuls of chocolate (I have small hands) to oil obtained from four Lecithin softgels.  Gently stir the chocolate until it is consistently melted. 

I also found that a tiny bit of coco power can give the chocolate a more balanced taste.  Just add a sprinkle to the batch.

I made a lot of chocolates, and I don't have a double boiler, so I experimented with several ways of melting the chocolate.

The first way:
A tall pot with half full of water.  I put a bamboo steamer basket on top of the pot.  I put a small glass mixing bowl on top of the bamboo steamer basket.  Chocolate melts go in the mixing bowl.  Paper towels go in the top of the steamer basket where it meets the glass bowl so that steam and chocolate do not mix. 

The second way (best way):
I kept the tall pot, bamboo steamer setup, but switched from using a glass bowl to a chocolate squeeze bottle. I also used a dishtowel to block the steam (see photos).  I only had one of these molds (molding material is expensive).   After I melted a whole bottle's worth of chocolate in the glass bowl I poured it into the squeeze bottle.  That way I could fill a mold and then heat it back up on the steamer when it was time to refill the mold.  Much less mess.

Step 9: Let the Chocolate Cool

Let the chocolate cool & hold at 96-98° F to work with the chocolate. This will probably take longer than you think.  Keep an eye on it and have your mold and tools ready.

If you are going to pour the chocolate into a squeeze bottle or funnel, do it while it is cooling.  Keep the thermometer in the chocolate so you can tell when it has cooled down enough to pour into the mold.

Note:  I tried a chocolate funnel before I settled on the squeeze bottle method.

Step 10: While Waiting, Start Printing the Candy Trays

While you are waiting for the chocolate to cool, you can start printing your candy trays.  If you don't have a 3D printer, you will need to plan for this or do with out the trays.  Print with PLA filament.

Again, the STL files would not upload to Instructables.   Here is the link to my OpenSCAD and STL files.  I did not write this code, I just used the parametric script to create a tray that would fit my chocolates perfectly.  Since I did not write the code, I will not paste it, just linke to it.  The parametric tray code was written by acker, who derived it from hippiegunnut

Step 11: Pour the Chocolate Into the Mold

Once the chocolate cools, get the chocolate into the mold.  You can use any of the methods described so far.  The pictures show me using the chocolate funnel. 

After you pour the chocolate into the mold, use a spatula or butter knife to smooth out the top of the chocolate.  Remove any excess on the top of the mold by scraping across the top. 

Step 12: Put the Mold in the Refrigerator

Put the silicone mold containing chocolate into the refrigerator until the chocolate solidifies. (about 20 minutes)

Step 13: Carefully Demold the Chocolate

These are a little difficult to get out. Wear candy makers cotton gloves to avoid marking the chocolate with your fingers.

Twist the rubber mold to loosen the chocolate. It will help to have small hands (I do and I am able to remove the chocolates without destroying them). I found that after loosing the chocolate by twisting the mold, it is easiest to twist out the face and rotate it out of the mold. Then grab the face and pull to remove the rest of the skull from the mold. You may smear the teeth a little, but overall it seems to work the best.

I have made many batches so far and I managed to get all of the chocolates out of the mold without destroying any of them.

Step 14: Place Chocolate in Trays

Step 15: Place Trays in Treat Bags

Step 16: Give Away to Everyone!

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