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Silicone (Rochow Direct Process)
Clay

Created by

Clay

22. September 2026DK
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Silicone (Rochow Direct Process)

Silicones - chains of silicon and oxygen carrying methyl groups - were known from Frederic Kipping's laboratory work, but could only be made a few grams at a time. In 1940 Eugene Rochow at General Electric found a one-step route: pass methyl chloride over hot silicon with copper, and methylchlorosilanes come straight off. Richard Müller found the same reaction independently in Germany, which is why it is also called the Müller-Rochow process. It is how silicones are still made. **US 2,380,995**, "Preparation of organosilicon halides", Rochow, assigned to General Electric, granted 7. August 1945, claims "effecting reaction between silicon and a hydrocarbon halide" with a copper catalyst at 200–500 °C. **Methyl chloride and chlorosilanes are toxic and stay in the plant.** You use the product: a two-part silicone mould of glass marbles, then cast hot wax in it, again and again.
Beginner
4 hours plus two cures

Instructions

1

Build the box

Cut foam board and hot-glue an open box 60 x 40 mm inside, 50 mm tall. Seal every inside seam with a bead of glue - silicone finds any gap.

Materials for this step:

Model Building Foam BoardModel Building Foam Board1 sheet

Tools needed:

Craft KnifeCraft Knife
Hot Glue GunHot Glue Gun
Steel RulerSteel Ruler
2

Clay bed and keys

Press sulphur-free modelling clay 20 mm deep into the box. Push two 16 mm marbles exactly halfway in, 20 mm apart. Press four dimples in the clay with a pencil end: these are the registration keys.

Materials for this step:

Modeling ClayModeling Clay150 g
Glass MarblesGlass Marbles2 pieces

Tools needed:

Digital Caliper 6-InchDigital Caliper 6-Inch
3

Weigh and mix

Weigh part A and part B at the kit's stated ratio into a mixing cup (the notebook gives the mass). Stir 3 minutes, scraping sides and bottom.

Materials for this step:

Silicone Mold Making KitSilicone Mold Making Kit1 kit

Tools needed:

Precision Digital ScalePrecision Digital Scale
Graduated Mixing CupsGraduated Mixing Cups
Stirring RodStirring Rod
4

First pour

Pour in a thin stream from 30 cm into one corner, never onto the marbles, until 6 mm above them. Cure for the kit's time.

Tools needed:

Graduated Mixing CupsGraduated Mixing Cups
5

Flip and release

Flip the box, peel away all clay and leave the marbles in the silicone. Brush a thin coat of petroleum jelly over the silicone face - silicone bonds to silicone.

Materials for this step:

Petroleum JellyPetroleum Jelly5 g
6

Second pour

Mix a second batch the same way and pour 6 mm above the marbles. Cure again.

Materials for this step:

Silicone Mold Making KitSilicone Mold Making Kit1 kit

Tools needed:

Precision Digital ScalePrecision Digital Scale
Graduated Mixing CupsGraduated Mixing Cups
7

Open and cut sprues

Tear off the foam board, part the halves and pop out the marbles. With the craft knife cut a 5 mm cone from the top face into each cavity.

Tools needed:

Craft KnifeCraft Knife
8

Cast wax

Melt paraffin wax in the double boiler to 75 °C. Band the halves shut, pour through each sprue, cool 30 minutes, open. Count how many casts it survives.

Materials for this step:

Paraffin WaxParaffin Wax100 g
Rubber BandsRubber Bands1 pack

Tools needed:

Double BoilerDouble Boiler
Candy ThermometerCandy Thermometer
Welding GlovesWelding Gloves
Clear Safety GlassesClear Safety Glasses
9

Troubleshoot the mould

Work down in order; each question points to one step to redo.

Flow

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10

Reaction, pour size, siblings

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History & Context

**What the patent specifies:** silicon reacted with a hydrocarbon halide over copper at 200–500 °C to give organosilicon halides. **Modern build (derived):** a two-part room-temperature-curing mould silicone. Silicone first served in the Second World War as grease and insulation for aircraft ignition systems; today it is sealant, bakeware, medical tubing and every maker's mould rubber. Its limits: it tears easily once nicked, is expensive, and a platinum-cure grade will not set against sulphur, some clays and latex gloves.

Materials

7

Tools Required

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