Conductive inks have a myriad of different interesting applications. As a quick, additive construction method for electronic circuits, they are especially intriguing. Unfortunately, for a long time they have been just out of reach of the hobby market. They are too expensive to buy in decent quantities, too complicated to make, too resistive to be practical, or require high annealing temperatures (which would ruin many of the materials you’d want to put traces on).
As with most things worth doing, there are risks.
NOTE: Please don’t do this at home unless you understand the risks and dangers and know how to avoid them. In fact, it’s best that you have a chemist or someone experienced with how to handle chemicals properly help you.
Ammonium hydroxide is nasty stuff. Formic Acid is even worse (It’s basically liquid pain. It’s the chemical in ant bites and bee stings that makes them hurt). Please respect this stuff.
See the material list, full process, and trial and error on Jordan’s post.