Usually, everybody use the old boy iron chloride for engrave his circuits.But that needs a machinery that costs between 50 and 700$.However, there is an other solution (that I use) in which you make your own solution.
You also need:
Chloridric acide Hydrogen peroxide (H2O2) at about 130 vol. Water
Then melt 1/2 water, 1/4 H2O2 and 1/4 acide.Be careful : those products are extremely dangerous so use glove, glasses, do not let childrenn paly with...
When it's done you have very few time so make it little by little. Then you have to feed your circuit into the solution just for 30sec.
You do not need to heat or so...it does it by itself.
Please do not reuse the solution since it won't work a second time!! (engrave will use more than 5min)