If you are new to wet plate, you'll learn that there are a number of different collodion formulas available. I've used the cadmium-free formulas of the two-part collodion + iodizer mixes from both B&S and UV Photographics. B&S sells one cadmium-free formula, whereas UVP sells two of them which are lithium based. I don't like working with cadmium since it is a known carcinogen. Cad-free formulas typically have a shorter shelf life, but since the clock starts ticking only after you mix the collodion (Part A) with the iodizer (Part B), you only mix as much as you anticipate using in the next few weeks or so. The cad-free formula sold by B&S is instantly useable as soon as you mix it, whereas both of UVP's cad-free formulas need to ripen for a few hours after mixing them.
As a side note, I used to make my own solutions with the raw liquid and powder chemicals, but it's much easier ordering the pre-mixed solutions these days... I spend less time measuring, weighing, and mixing chemicals with magnetic stirring rods, and more time shooting.
One other suggestion, as you alluded, is to gain competence with tintypes before attempting ambrotypes. The glass requires preparation and cleaning, and unless it's done well, images can lift off the glass during post-development washing. Wet plate work involves enough frustration already without adding the additional requirements of ambrotypes at the beginning of the learning curve.
(Incidentally, my avatar image to the left is one of the first plates I made at home after I got my training in wet plate at the Penumbra Foundation's Center for Alternative Photography in NYC back in 2011. It's a staging of Narcissus gazing at himself in the mirror. It took several tries, but eventually I got it right.)
I dream in black and white.
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