Thanks for the replies!
ferrix, I'm mostly working with graphite and nickel powders. It's all pretty benign, although some people are sensitive to nickel and I could imagine that if they stuck the stuff to their skin it could irritate it after a while. I'm working on the conductivity, and hopefully I'll be able to beat wire glue's 13.16 ohms per cm^2 (although I still haven't figured out the best way to measure conductivity of a putty, since it's not spreadable like a paint. Maybe contact resistance per cm^3?)
abaxas, it's...probably not edible? It's not on the Kickstarter page because I didn't want to make any definitive claims either way without further testing. It's not certified non-toxic, but none of its constituent parts are toxic. I haven't eaten it myself, but the polymer is the same used in chewing gum, and graphite is fairly nonreactive. The trouble would be the nickel, I'm not sure what would happen if it were ingested. Swallowing an old nickel coin is probably okay, but the putty may have more nickel surface area because it's a powder. Best not to try until I get an MSDS