Silicone rubber is a great material for making architectural models, especially ones with unusual shapes, like domes. Models can be colorized with clear silicone and powdered pigments, since paints do not stick to silicone. The models are waterproof, light-weight, and pretty much unbreakable.
This is a very useful material for architectural model making and should be taught to all architecture students.
Step 1: Tools and Techniques
100% RTV silicone rubber comes in grease gun cartridges from the hardware store. Some standard colors are clear, black, white, aluminum, and bronze. You can mix custom colors by extruding clear silicone onto a palette and mixing in powdered pigments with a palette knife. The colorized silicone can then be spread on with a palette knife, gloved hand, or sacrificial paint brush. You can also pack it into plastic-tipped syringes available at pet stores for finer details. They come with curved, conical tips that can be cut at different locations to change the size of the extrusion.
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.