Ferric Chloride is not an acid, but a chemical salt that works like an acid. I like it because it works slowly, and leaves clean lines and a deeply etched reflective surface. It should be used in a ratio of 1 part ferric and 4 parts water.

Set up a container that will accommodate up to 10 pieces, as it is advisable to etch more than one piece at a time. The solution should just cover the pieces.

A aerator for a fish tank should be used to agitate the solution. This is because the ferric chloride is heavier than water, and has a tendency to fall to the bottom. The aerator hose should be fixed in the centre of the container.

The container should be plastic, glass or ceramic. A lid is advisable since the air hose causes it to splatter.

The pieces should be paced in the vat leaning up against the side. After 2 hours in the solution they should be removed and checked to make sure they are etching properly. It is advisable to scratch any areas that are not etching properly (sometimes the rosin  melts out of the resist and is not noticeable until the etching begins.)

When the pieces are replaced in the container, they should be put in a different place, and turned a quarter turn. The air hose tends to set up currents, and if the pieces are left in the same place they will be etched unevenly.

After 4 more hours, they should be moved and turned another quarter turn.

After 6 more hours change and rotate again.

After 8 more hours they will be finished.

You have the option of doing a further step. This involves attaching the piece to a piece of Styrofoam, and floating it upside down in a fresh batch of full strength ferric for 20 minutes. This adds an extra level of texture.