I've just replaced by tailgate as the old one was rotten.

The glass on the new one is much darker, and has "opticool" on the info plate.

However there is a damaged area about the size of a thumbnail right in the middle where what looks like window tint has peeled off.

Anyone know if the opticool glass has a coating applied that could peel off? Or is it just normal glass and someone has applied standard window tint?

I don't want to start trying to peel it if it's supposed to be part of the glass! But if it's tint ill probably just peel it.

Optikool has a light green tint and is said to be solar absorbing and reflecting to reduce the amount of heat getting into the car on sunny days. Being approved for use on windscreens it can't be very dark. 75% transmission measured the approved way is the minimum allowed. Due to the way human eyes compensate for light level changes that looks a lot lighter than the raw figures suggest. I'd be unsurprised to discover that Optikool is in the 90% transmission region.

https://www.pilkington.com/en-gb/uk/automotive/original-equipment/automotive-glazing/automotive-products/thermal-comfort

If you have a tint layer applied to it it will be much darker than you'd usually expect from the tint alone.

Clive

Okay. I suspect it's tinted then! Looking out it has a very distinct blue shade.
Must be a professional job as even with the plastic trims off I couldn't see any edge. The only giveaway (other than the peeling damaged but!) Is some halos around the "dots" at the edge of the glass.

I actually quite like the dark tinted look now it's on the car, but given it's damaged and only one window I guess it's better to remove it for now

Original "dark" windows have something embedded in the glass. If it peels off, it must be film.
The "halos" or "bubbles" around the dots on the edges - and in the lettering - are the giveaway.
If you are happy with it, and does not look too shabby, I'd keep it.

If you want to take it off, get a hair dryer or a heat gun (careful!) and slowly and evenly pull it off after warming up the glass, to help dissolve the glue. Pull slowly is the trick. You can use glass cleaner for any glue residue.

I got it off, was definitely a tinting film. Horrible to remove though, it broke up into tiny pieces and wouldnt pull cleanly. Also left loads of horrible residue. Been over it twice with "Elbow Grease" cleaner and a going over with brake clean which has improved things, but i need another few passes over it to get it all off.

Ahi Ahi ... now I remember the upper tailgate glass has the electricals for the demist.
Don't go too hard on those or it might lose the capability to demist/defog the window - try it.
Brake cleaner is very aggressive on plastics/rubbers on the edges, use a degreaser or window cleaner instead. Less powerful, but less damaging ..