Linda, I spent about 30 minutes searching for this information
because I am avoiding doing some loathsome accounting tasks. Lucky
you. I like to use Google when searching the WWW: www.google.com.
First though, here's an Orchid posting by Karen Christians, who has
extensive etching experience:
I don't know if Karen starts with ferric nitrate crystals, however.
Perhaps Karen is reading and will clarify.
The next link points to an entry on a MEMS message board; I have no
idea what MEMS is. But, the writer suggests 10 grams or less "per
liter". Per liter of what he doesn't say, I assume they mean per
liter of water.
And here's a link to a table that lists metals and etchants:
If you understand what Baume is, then it probably gives a recipe.
Or, you can probably find out if you continue searching. I've
procrastinated long enough!
Christine in Littleton, Massachusetts, USA, which has been
transformed into a winter wonderland by a late winter dusting of snow.