Introduction: Silicone Mold Making for Soap

For a school project I had to make a soap that would have my project's logo on it.

This instructable was made by a DIN 2012 member

Step 1: Making the Logo

To make the mold, you need to make a plastic model of what you want the soap to look like. This model will be cast into silicone which will be the actual mold so you don't have to flip the side of the logo.

To make the logo, I used a laser cutting machine. You have to have a version of the logo on Illustrator. I had to simplifie the logo. The silicon will take every little detail, but the soap is not as permissive.

Make the logo 5% bigger than what you want to obtain. The silicone doesn't shrink much, but the soap does.

I used a sheet of cast acrylic for this part of the model.

Once cleaned, you should obtain something like this.

Step 2: Making the Soap Model

In order to have the general shape of the soap, I made a polystyrene model of the soap on a metal lathe. A wood lathe could do the same job. Instead of the polystyrene, you could use acrylic or even clay (make sure there is no sulfure in it or the silicone won't cure). You could use about anything that is non-porous.

I did the soap in two parts to be sure it would work. In the end I will have two molds: the top with the logo, and the bottom (by which I pour the soap). In the upper part (shown on the right) I left an empty space for the logo.

Again, make the model about 5% bigger than wanted to compensate for the shrinking of the soap.

Step 3: Preparing the Casting

With a hot glue gun i glued the model on a sheet of polystyrene. Around each of them i glued a piece of  polystyrene in a circle, forming two distincts cavities of same size.

Make sure you don't use to much glue under the models or silicon might infiltrate underneath.

Make sure you use a lot of glue around the cavities or silicon might leak out.

Step 4: Casting

To make the mold I used the Mold Star 30 by Smooth-On.

It's an easy to use product. all you have to do is mix equal volumes of part a and part b liquids and mix. You have plenty of time to act and it takes only 6 hours before you can release the mold. As it is silicone, i did not have to use release agent, but you shoul do a test before. You can use an old paint brush to 

Make sure you use disposable cups because you might not be able to use them after. Once cured, the silicone is not dangerous, but before you do your casting make sure to read all the instructions and warnings.

Step 5: The Result

Six hours later you can release you molds. You should have something like this!

Step 6: Casting the Soap

The soap i used is microwaveable. I melted it in a ceramic cup, and poured it in the mold. To ensure there was no bubbles on the surface of the soap I brushed it, while still very hot, with a paint brush.

Be careful, the soap can be very hot!

Let stand for at least 20-30 minutes before opening the mold.

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