Some of these tips may sound like common sense, but...

“Top 10” Things NOT to do to a pinball back glass:

1 ) Don’t store back glasses in areas of extreme temperature changes (hot/cold) or keep them in areas such as vehicles, garages where they are exposed to rapid changes (even overnight). If you do, you may find a surprise waiting for you the next day. If your games are stored in a non climate control garage, be mindful of the temperature range that exists. Does the winter cause the temperature to drop lower than 30 F? What are the humidity conditions? What is the highest temperature that is normally existing in the summer? Is it higher than 80 F? Is there proper water drainage in the garage? Block and black out all windows in a garage. These are the primary source of temperature changes outside of weather and allow for fading of colors. Seal doorways to prevent moisture from entering and use barrier materials to prevent moisture from reaching cabinets of machines as well. One single year can do more damage than people ever realize. If you have games upright without legs on, make sure you use pallets. Never leaves on the floor for long periods of time, as both moisture and temperature will cause problems.

2 ) Don’t “free hand” back glasses (one hand) when removing them or moving them out of games, and always use the two way "offhand" hold, preferably top and bottom, not side to side to avoid "flexing"

3 ) Don’t put back glasses in direct sunlight (meaning don’t put the games next to windows) as the inking will fade over time

4 ) Don’t use varathane, urethanes, lacquers, or clear coat paints or finishes on back glasses, they will melt and destroy the ink, or at best case shorten the lifespan of the ink layers due to different expansion rates or yellow the paint. You should not "clear coat" back glasses. If you see an old can of "Save Your Glass" throw the product away, it is destructive! Additionally, do not spray glass cleaners, deodorizers, or other products on the backside of the backglass with the ink screening, it will damage the paint! It is dangerous to "clean" dirt off a backglass in any shape or form. Even translites can be damaged this way, if not careful.

5 ) Don’t install back glasses in games without protective edge trimming on all sides AND a lift channel, or you risk chipping or breaking them

6 ) Don’t “force” a back glass into a back box, something is WRONG (did you forget to undo the lock?)

7) Don’t do full coating of back glasses with Triple Thick Crystal Clear Glaze or water based acrylic clear, if the game remains in proper environmental conditions, you are not putting back glasses in long term storage, or they are not delaminating, it is not necessary. Do not use the recently popular "saran wrap + KTTCCC" method, it does NOT work, makes a mess, and makes the glass UNREPAIRABLE for future use. Do not use any type of tape for "masking", as you WILL LIFT PAINT.

8 ) Don’t use mylar unless you really have to and if you must do so in small spots, as it may never be able to be removed without lifting the inking and it makes future restorations difficult.

9 ) Don’t put back glasses down on hard surfaces such as floors EVER, and NEVER lay them flat, always store them upright

10 ) Don't attempt to peel, "pop", or re glue a veining, cracking, or flaking back glass, seal the damage before it spreads by spraying the glass with TT or brush on acrylic sealer.

FINAL BONUS POINTS: Don’t use incorrect rated bulbs in back box light panels that produce excess heat (LEDS can be a superb alternative if used tastefully), in order to prevent discoloration and damage. Remove all #44 and replace with #47 at minimum if these are used. Excessive bulbs in certain games can be just removed all together, by using half the number in the light panel and generate the same effect.

Lately, I have seen more crazy things than usual.
Keep those backglasses safe!

This is a pinball "public service announcement".
Feel free to provide additions.

It depends on the nature of the damage, how much damage has begun to occur, and where the damage is located on the glass.
Send me a PM with a link to a large and clear, backside photo of the ES glass, so I can evaluate which method would work best.

Sounds like a combination into #8.
If I am working on machines, I put them out of harm's way, so nothing (or me) can bump into them while I am working on the machine.
A towel or heavy cardboard is a necessity.

There is one method that provides permanent protection and prevents ink screening from ever being damaged due to environmental changes, but it can be expensive and needs to be applied by someone that knows what they are doing, or it may turn into a pile of goo.

This method requires to encase the backside of the backglass in a thermoplastic film coating, similar to what is being done by BGRESTO for application films to repair backglasses but in "clear liquid form".
This is not a "brush on" or "spray on" application.
It is a "hot" application, similar to aspects of clear coating (but not the same thing), and completely covers the entire backside of the backglass similar to what AGC did in the 1990s, but is MUCH better quality, and resists heat cracking.
In essence, the layer bonds to the the existing ink screening layer at a molecular level, not via adhesives.
It provides a permanent vacuum sealed layer against air contact and exposure to the environment, durable and scratch resistant, flexible and expansive on temperature changes, does not effect translucency, and is non-permeable against liquid contacts.
This was not an option "back in the day" when most backglasses were made.
The only way the backglass is going to be ruined is gets broken by someone being stupid.

I have used this method on some of my rarest and expensive backglasses, but the cost exceeds $300 an application, which is not generally suitable for most glasses, as that normally equals or exceeds the cost of the backglass itself.

I will dig up a video of the application process when I get the chance.
I still keep tabs on posts I write.
The key is finding the right person that knows the understanding of using the material on GLASS versus metal or wood, due to expansion and contraction rates and maintaining temperature control.
Otherwise you can end up with a pile of shards or a spiderwebbed piece of garbage.

I recently saw someone conduct a test on a video using clear saran wrap plastic and triple thick.
VERY BAD IDEA.
One, it does not work and is not effective.
Two, the results look like a$$.
Three, the glass comes out more damaged than the original condition.
And Four, the backglass can never be restored or repaired.

I recognize the backglass easily, Bally Mystic.
I may be able to help you out other than your question, as I own a very nice used glass framed on one of my walls with no cracking or veining. It was a second hand purchase on a game that got parted out.

I would need to get it scanned, and let BGResto do the rest of the work for you.
It has the 3D insert installed, so it would need to be removed from the scan with Stephen.
I have no idea what cost or time would be involved on this game backglass.
Keep in mind you are going to lose ALL mirroring on the reproduction, that will be turned to grey.
This is NOT insignificant on this game title.

Back to the question at hand.
Do you have the missing pieces of artwork?
How DRY is the ink screening?
These are most critical aspects.
If you have the missing pieces, this backglass is at least partially recoverable.
Place the pieces "puzzle style" back into the glass.
Use a clear acrylic and a brush for a *light* coat on key locations to make broken pieces "stick".
Use a thinner clear plastic one sheet film (non-adhesive) on the ENTIRE glass and lock it down on all edges with clear epoxy, not saran wrap because wrap will stick to the ink screen pieces, tearing them.
Make sure the film has all static removed from it as well.
If you work from one side to another and "pull" the clear film across, carefully, you should get a very good seal without damaging the artwork.
It will not of course be anywhere near the quality of a vacuum seal.
This is the best you can do without professional assistance and the right equipment.

Every backglass situation is unique terms of restoration. My backglass is not for sale, but I do lend them for reproduction efforts. If CPR chooses to do a potential run, this is one of several that could be used.

The film can be purchased at craft stores. You are looking at thicknesses less than 1/32th of an inch, in order to make it manageable.

I would still use acrylic clear with a brush in any problematic areas that may chip out.

An new addition based on recently incorrect recommendations I saw on another forum website:

Do not spray glass cleaners, deodorizers, or other products on the backside of the backglass with the ink screening, it will damage the paint!
There is no product that is designed with this in mind.
Any cleaner with ammonia is especially bad.
Pet store furniture cleaners are not meant for cleaning pinball backglasses!
Any bleach products will eat paint too!

It is dangerous to "clean" dirt off original 20-50 year old backglasses in any shape or form.
Leave it alone, you will be glad you did when your rag cracks 40 year old dry paint at best case leaving the damage visible on the front side.
You will have a very sad face.

Even translites can be damaged this way, if not careful, especially around areas that have scratches.
If a translite (not backglass) needs cleaned, use a mild soap and water (Dawn) solution with a soft terry cloth rag.
Do not use Simple Green in pure form ensure it is diluted first for a "tough spot".
Do not use Mean Green!
Do not use Goo Gone or Goof Off (including removing tape or other residues)!

If a glass needs to be "fumigated" use crystal air deodorizer in a cup, and keep in the backglass in a closed mini paint booth, artwork side UP for a couple of weeks under dry, room temperature conditions. The smell will be purged, then deal with existing backglass damage.