Yes, silicone caulking can be used to make molds. I will give the recipe, but then I will explain why it isn't the best option, and why ComposiMold is a much better option. 

The recipe for using Household Items for Making Molds:

1. Buy 100% silicone caulking. This is the GE Silicone 1, material: you can find it on Amazon here $4.75 for 10 oz.

2. Squeeze it out into a bowl

3. Mix 5 tablespoons of cornstarch into the silicone. This adds moisture to the silicone, which is why the silicone cures.

4. Wipe our original shape with a mold release, such as vegetable oil or vaseline.

5. Pour the silicone over the object you want to mold

6. Let cure. This material has the random name of Oogoo. It's pretty neat

Why isn't silicone caulking great for mold making?

1. Shrinkage. Oogoo shrinks up to 30%

2. The price adds up. 10 ounces gives you 1 small mold

3. Not reusable

4. Not great details. It's a thick goo. Details are lost.

What should you use for mold making?

ComposiMold, 

• ComposiMold is a less expensive (definitely cheaper in the long run) rubber mold for plaster casts, plastic casts, and others. 
• The rubber mold is much more forgiving in terms of allowing you to fix mistakes (Reheat or use a heat gun to heat an area). 
• The silicone molds are typically longer lasting for single rubber molds, although after they start to go bad, you can not fix them or recast them. One of the initial ways we started using ComposiMold was for a backing to brush-on silicone mold making materials and polyurethane molds because you can use very little of the silicone mold material and reduce the mold making costs.
• ComposiMold is reusable and much better for the environment.

So keep the OOGOO FOR the Casting.

What types of Materials can be cast with ComposiMold?

You can use many casting materials in the ComposiMold rubber molds including: plaster or gypsum, concrete: Use as thick a mixture as possible to give stronger castings: Because ComposiMold is biodegradable, if the solution is too liquidy, you may damage the mold details.

Plastics: look for urethane or epoxy resins that cure slowly to reduce the heat created during curing.

Chocolate: works awesome: white chocolate, dark chocolate, tasty chocolate

Candle wax, and soap! Freeze the ComposiMold first so that the wax or soap will cool faster than the ComposiMold can heat up. Many others!

ComposiMold melts at 130 F. Any casting that creates heats up to more than 130 F can melt ComposiMold, but there are many ways to get around this limitation. Examples include:

• Pouring in intervals so each pour only creates a little heat and the heat can dissipate
• Adding filler such as dry talc, other dry powders, wood chips, etc. to the casting material so there is less casting material to create heat
• Freeze or Cool the ComposiMold prior to pouring in the casting material if it creates a lot of heat or is hot. The heat during curing can sometimes be removed faster than the ComposiMold can heat up. This is a great way of doing candle wax and soaps.
• Using a brush-on mold making material such as latex, urethane rubber, or silicone to create a barrier. This also helps create molds that can last for many more castings. This allows 90-95% of the mold to be reused whiles still getting the benefit of longer lasting molds.

Can ComposiMold be used to cast silicone objects?

Yes, spray your mold with a silicone mold release and mix your silicone according to the instructions given on the container or flyer (different types of silicone have different mix ratios). Then pour your silicone mixture into the mold and wait for it to solidify before removing.

Can I use ComposiMold for polymer clay push molds?
Yes, we recommend using the ComposiMold-Firm or ImPRESSive Putty for polymer clay push molds because of the higher stiffness. Make the mold as you normally would using ComposiMold. Press in the clay to make the shape. If necessary, place the rubber mold into a container to provide stiffness to the rubber mold while pressing in the polymer clay.

Can I produce a ComposiMold mold from a wax, Plasticine, Castilene or Monster clay sculpture?

Yes, wax and wax based clay sculptures typically have a melting point of about 160 Fahrenheit. Before pouring ComposiMold over your sculpture, make sure the ComposiMold is not too hot, wait until it reaches 145 Fahrenheit or less before pouring. If you want to be extra careful not to ruin your sculpture cool it in the fridge or freezer.