Gum Sandarac dissolved in alcohol is the recommended coating for Tintypes, as it has been the historical choice.
However, people in the 1860s didn't have Spray Lacquer, Enamel, or Shellac. Would any of these also work as a coating. My suspicion is that they'd work better, as they'd be a much purer sample and clearer than homemade gum sandarac solution.
Some people say shellac is historical more correct. With historical used products you know they stay good for a long time.
Can you heat dry spray lacquer or enamel?
I sometimes use renaissance wax on plates, apply it with cottonpads, nice and easy can be repeteated when necessary. and I have the impression that the plates stay a bit lighter.
I don't think it would be recommended to heat dry lacquer or enamel, too hot a temperature and it'll start bubbling. But is such a step necessary? Couldn't you heat dry the bare tintype, then spray with enamel and let it dry naturally? Spray enamel, like Krylon Crystal Clear dries within 10min at room temperature.
Renaissance wax sounds interesting, but my belief from what I've read was that the plates are too delicate for direct touching. What has your experience been?
Resuscitating this almost year-old thread, I am very interested in finding alternatives to Gum Sandarac. It's very hard to find here in Brazil... I've been looking around and still can't find it.
I've used Shellac for several years and find it much better and easier to work with than sandarac.
I use this recipe:
100ml alcohol
12g shellac
5ml lavender oil.
No need to preheat the plate like with sandarac, just pour it on, pour it off and stick it in a toaster oven at 180 for 5 minutes. Comes out hard and dry but you should let it sit for a week before wrapping it in anything.
An alternative formula, I have used this for negatives. More lavender oil makes varnish more susceptible to scratches, you can try it with you nail. Less lavender oil makes less flexible much harder varnish ideal for collodion negatives.
12.5 gr Shellac
1.25 ml lavender oil
100 ml Ethanol