Picture of Ice Crystals: Food-Safe Molds from a 3D Printed Object
This Instructable covers the process of making a food-safe mold from a 3D printed object. I will provide two methods for making an ice mold (one being a tray), and some of the steps can be mixed and matched. My chosen forms are large and small crystals - I thought a large crystal would not only look awesome/appropriate in a glass with a high-priced beverage, but also would take longer to melt.

One additional note: for best results with large objects I recommend designing your object for use with a particular glass, the reason being that your object will float with the addition of liquid UNLESS it fits perfectly snug into the glass (of course it will eventually melt, but will look totally awesome for a short time :).

You will need:
(1) A 3D printed object
(2) Food safe material for mold. I used Smooth-On's Smooth-Sil 940 as well as 1/8" Polyethylene sheets from Tap Plastics
(3) Release Agent
(4) Plastic Container & Stir Stick
(5) Glue Gun
(6) Nitrile or plastic gloves that ARE NOT latex
(7) Scale (Smooth-Sil 940 uses a material ratio of 10A:1B)
(8) Sandpaper or Sanding block (grades 180, 220, & 400)
(9) Clean surface

For intermediary objects (explained later):
(1) Cheaper silicone than Smooth-Sil, such as Mold Star (which de-airs itself)
(2) Smooth-Cast 325
(3) Plastic Container & stir stick in addition to relevant items mentioned above
Recommended: Pressure tank and compressor

If you decide to make a tray as opposed to a mold you will need access to a vacuum forming machine. Alternatively, you can build one: check out this great Instructable.

Note 1: Thanks to HexCorp in Tarzana for letting me use your space and 3D printer, a great makerspace is emerging! Thank you to UC Santa Cruz for continued sponsorship as a research associate and owning a vacuum forming machine.

Note 2: I am in no way affiliated with Smooth On, Autodesk, Makerbot or any other company mentioned in this Instructable and receive no compensation
for the publication of this Instructable by either of the aforementioned companies.

awesome instructable!!!! I just made a vacuum former and am curious if the second mold is a necessary step. I have been having good luck vacuum forming directly onto ABS material. I'm just curious if this affects the "food safety" aspect of the mold or if your doing this due to the low melting point of PLA?

danm_daniel (author)  steven.d.holland9 months ago

If you are able to produce a "negative" of the desired form in a styrene sheet, the second step is not necessary.

As far as food safety, its always wise to get the MSDS (material safety data sheet) for any raw material you're intending to use as a molding agent, especially if you desire a food-safe mold (usually these materials cost a little more and are explicit in their instructions). That being said, there are food-safe Styrene sheets available for vacuum forming through a number of distributors (one I know of is TAP plastics), however, I am unsure about the food-safety of Acrylonitrile-Butadiene Styrene.

I like this very much. If you would like your ice-diamond to look even more crystalline, check out this instructable:
That's a great instructable to use in combination with this one, thanks for sharing!