Good work, Karen and Gadget
Revised date: first half of 1870s. At least that's what the lady's clothing suggests to me. It could be later but she does look like a fashionable gal
Re. preserving: you need to be able to stop the plate from flexing, so keeping it wrapped in good-quality paper, and lying it flat in a box is a good way to keep it safe. Alternatively you could have it framed by a very good framer (look for someone specialising in Conservation Framing) who knows what they are doing with old photos such as this. They will probably sink it into a card mount and then put it in a frame, so it's not glued to anything, and is nice and stable and well-protected.
The emulsion on these photos is generally pretty stable, but it's very prone to scratching (as you can see from your own) but the bases are made of iron, so they can rust. Keep it somewhere dry and cool and you shouldn't have any problems.
Hope that helps
Prue
