Varnish on tintypes, wet plate, or liquid emulsion

Can a varnish bought from the hardware store be used for tintypes, or any of the other emulsion on metal processes? I've seen the formulas using gum sandarac, oil of lavender, flame, and such.
Is there a specific reason people use these varnishes, other than tradition?
Can the modern products be used effectively?
(Why do I get the feeling I'm going to be flamed for asking this question......)
Just curious.
Thanks,
Steve
www.scdowellphoto.com

Steve, There are a few people experimenting with across-the-counter varnishes with mixed results. If you look at the old literature you'll find at least 5 or 6 formulas from back then that people were using other than the sandarac formula. So I wouldn't worry about getting flamed for asking a good question. I use the sandarac formula because it is cheap, easy to make, and produces beautiful results. A lot of questions arise about the long term effects of across-the-counter varnishes but I'm all for someone who can come up with a better mouse trap. If you go to the wet plate forum you'll find pages on this discussion with some recommendations for across-the-counter varnishes. Another perk of the sandarac varnish is that beautiful lavender smell it produces while varnishing. Plus when varnishing a plate for someone in the field it is ready to go after the final heating to set the varnish, where the across-the-counter varnish takes a day or so to set up. I'm far from being a reenactor/traditionalist so I say use what ever works best for you.