I am also very curious about this. I've been told to use a Krylon spray, but am also wondering what the pro/restoration veterans think.

Haha I misread the title as "advice on STEALING a backglass." Much different thread

There's some advice in this thread: https://pinside.com/pinball/forum/topic/concern-about-using-triple-thick-on-backglass

There will certainly be a plethora of opinions on this subject. For back glasses I have two opinions... LED's to reduce heat and Krylon Triple Thick for preservation. I have had my best luck coating with Triple Thick at lower ambient temperatures as the Triple Thick likes to crystalize quickly if it is warm out. To minimize the crystallization (note...I also spray right over the score windows), I use two cans of Triple Thick at once. Using two cans enables me to get a single very wet coat down in just one shot.

I heard that Krylon Triple thick in a changing environment will kill that glass. Triple thick is mean to be used on a glass to seal further damage. However, the glass should be inside the home in a more
stable temperature environment.

I think that the changing temperature will cause spidering to occur. Triple thick will expand and
contract with the changing temperature which will cause movement of the decal on the glass. Not a good story. If you need to keep it in this environment, try getting a translite print and keep the glass
indoors.

I would leave it alone
the backglass is now 35yo, it has survived temperature variations

why risk tampering with it?

Agreed. Get the backbox GI converted to LED and you will eliminate the risk of the bulb heat causing damage.

Considering the reports we are now seeing on triple thick I would avoid it unless you have a problem.

-Jay

I wouldn't bother doing anything with it.

Ain't broke don't fix it - obey the law.