This is a bottle of Conductive Ink. Thanks to Jordan Bunker & co we can show you how to make it:
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).
It goes without saying, but still must be said: always be careful when attempting Science in the kitchen.