This is THE BEST chemical to eat away exposed copper on copper clad board to make a pcd. you can draw you traces with a Sharpy, or, even better, you can buy LASER printer transparencyies, print a mirror image of your board, then place the transparency on the copper and iron it on good so all the tiner transfers. Anywhere covered is protected, weather you use permenant marker, toner, petrollium jelly, KY jelly... Well, im not sure about the last product for PCB, but its good to have on hand. LOL