This is a very useful material for architectural model making and should be taught to all architecture students.
Step 1: Tools and Techniques
Be careful not to injure your thumb from pushing too hard to extrude silicone through small syringe tip openings. I usually put a big washer around the syringe to give better purchase for my fingers and then push the plunger with the heel of my hand, if the pressure needed is too much for my thumb. If worst comes to worst cut your extrusion opening larger with a knife so there is less pressure needed. You will sacrifice some details from fine extrusions, perhaps, but your thumb will survive to work another day.
Polyethylene plastic makes a good non-stick surface if you want to spread out flat layers, or draw designs, and then peel them off to work with them. You can stretch and tape plastic trash bags over cardboard or masonite to work on, but my favorite work surface is a rigid polyethylene kitchen cutting board I got from Sam's Club.
You can draw with silicone in the air, to some extent, sticking it to hardened silicone already in place. You can also make shapes out of styrofoam and cover them with a layer of silicone.
Step 2: The Castle
The walls were built up with extrusions of clear silicone straight from the grease gun cartridge it comes in and then colorized by rubbing on clear silicone with powdered pigments.
I remember making clay castles in elementary school, which was fun.
Step 3: A Domed House Model
This model was built up by laying new extrusions onto old ones in horizontal layers, or next to hardened lines in the air. Some of the arches were first drawn on a non-stick surface, peeled off when dry, and then tacked in location with silicone. Extrusion lines were then stuck onto them to fill in areas in the air.
It was done with extrusions of clear silicone directly from the grease gun cartridge it came in, and colorized later with pigmented clear silicone using a rubber glove, or a sacrificial paint brush. Forget about ever cleaning the brush after use.
As you can see from the photos, the model can be crushed and then spring back into shape. It is basically unbreakable, and light-weight -- good advantages for transporting the model or mailing it.