Human-human interactions are usually more intimate, compassionate, and emotional than human-object interactions. But what if we put some human element into the mundane, unintelligent everyday objects? In this instructable I made soaps in the shape of my hand, which requires a more humanly interaction from its users.
Step 1: Life Casting My Hand
First I did a life cast of my hand using alginate. Alginate is a super cheap and easy-to-use life casting material. The only downside is that it's super fragile thus can only cast once. It sets in 10-15 minutes, so it's not too painful for us to hold our body parts in a still position. I used Smooth-on Alja Safe alginate. Follow the instructions for mixing alginate and water, usually it's about 1~1.5 to 1 by volume for alginate powder and water. Use a mixer tip with a hand drill to mix fast and thoroughly until it's consistent without lumps.
In 10-15 minutes the alginate will set and you can feel it. (You can raise the casting container up with your hand) Carefully pull your hand out of the container. Remember that alginate is super fragile and easy to break so be super careful to keep the alginate intact.
Now with the alginate mold we can cast our hand in a more durable material. Why do we need a more durable version of our hand instead of using our hand directly? Well it's cause our human flesh won't stand a lot of casting materials (both in terms of contact allergy and curing time) so to have a more durable version of our hand will just come in handy.
For this casting I used Rockite cement. You can also use a variety of plasters (plaster of paris is not recommended though). Rockite sets in about 15 minutes, and then you can destroy the alginate mold and dig the hand out.
Step 2: Make Silicone Molds
With a more durable hand, we can now make a silicone mold which will eventually used for soap casting. The process of making a two part silicone mold can be found in this instructable. I used several different kinds of silicone and urethane in my experiments (to use up left-over materials and save money), and found little difference in this application.
Here's a list of materials I tried:
TAP Plastics Urethane RTV (no degassing, cured material on the rigid side which holds shape well)
TAP Plastics Silicone RTV (no degassing, translucent, fast cure time, very flexible when cured)
Smooth-on Mold Star (no degassing)
Smooth-on Sorta Clear (degassing needed, translucent)
Step 3: Support Design
Before we jump to soap casting, we need to plan how to attach the hand to a wall surface first. I designed a simple part that will serve as an inside structure for the soap, and also connect it to a base, which will be attached to the wall by commander tapes.
To make it funnier, the support part has a tiny hand on it also. So when the soap is used up, the tiny hand inside will be revealed. The parts are 3d printed on Objet 3d printers using Vero clear material.
Step 4: Soap Casting
Clean the silicone molds and secure them in place with rubber bands. Now we're ready to cast soaps!
I used melt and pour soap base, and added some mica powder (pearl) to give the soap a sheen. Use a small pot to melt the soap base to a liquid state, and then pour it into the silicone molds. After I poured I put on the support bases on and secure them in place using tapes.
Put the whole thing into your fridge (not the freezer) and wait overnight or longer. Once the support bases are firmly connected to the soap body, you're ready to demold your soap.
It's very likely that it will not be a perfectly clean cast, but no worries, it is super easy to clean the cast and even sculpt it a little bit because soap is so soft. I used a few clay sculpting tools (also used in 3d print cleaning) to clean the seams on the side of the fingers.
Step 5: User Testing!
Soaps are supposed to be used! I installed three soaps with different gestures in the bathrooms at Pier9 workshop. It's fun to see people interact with them in the bathroom. And needless to say, I very much enjoyed "being touched" by people!