None of the above !

http://www.polymerclay.com.au/kscc500kryloncrystalcleartriplethickglaze0500noexpress-p-11483.html

I've been using this for over 10 years and never had an issue.

don't remove any sticky tape etc - as this was most likely used to hold the backglass art together. Removing it will remove the paint.

Triple thick glaze is the best by far. Get it at most artist and craft suppliers for about $18 (I think). Check youtube for correct application to backglass. A can should do 3 or 4 backglasses if you apply 3 -4 light  coats criss-crossed. You will preserve the backglass for at least 20 years or more.