To use aqufortis, first you saturate the wood with it and let it dry. It will turn your wood pea green but don't get alarmed. After it dries you blush it with a heat source, I use a heat gun, be careful to not char the wood. It doesn't take much heat to blush the stain, your wood will turn dark tan. Still looks kinda' pukey but when you put the finish on the spectacular results pop up.
After you blush the stain it is a good idea neutralize the aqufortis with a dilute lye mixture of a tablespoon of lye in a cup of water. Wipe the lye on, then rinse the wood with water. If you don't neutralize the aqufortis there is a chance it will keep working and your wood will get darker and darker over time.
The above process is probably more than an average bow maker will want to go through but the results are pretty amazing.
Here is a before(left) and after(right) blush picture.