Can Someone Help Me Understand These Glue/Adhesion Marks?

I have two sets of questions; the first relates to the following stamp:

At first glance it looks "mint-hinged"; it has a kind of shine on the surface and a hinged back - although uncancelled, is this actually a used stamp (due to the shine on the front or the anomalies on the back)? Is the surface shine due to glue or from the ink? My next questions are in the post just below...

The question I posted above relates to my next question, which is: can someone help me interpret the marks around the affixed stamps? I ask in order to understand if the marks are simply a) age marks, b) water marks from a water pad (to wet the gum side of a stamp), c) actual adhesive material like glue?

I start with this image, which shows a surface shine similar to the stamp I posted above - is this from glue or from the ink? There is no shine/residue on the cover itself, only on the stamp



This looks like a paste-up and around it and on the surface is a shine - is that adhesive glue?



The following 4 covers exhibit dark marks near/around the stamps - what is that?





This is a cut out affixed to a cover. I imagine that the marks around it are standard glue?

Bad husbandry'

Classic "toning" or "Rust" marks, indicates storage in an humid environment, it generally begins at the fine hairs of the perforation teeth.
Very common.

The first stamp, is mucilage (gum) that has lost its viscocity in an humid environment, then re-hardened / re set in a stamp mount, giving it that flat mirror looking shine.

The rest could be anything, depending on the owner at the time.

The last item would probably be private gum of some sort, as the item is a mutilated stationery piece, affixed.

Thanks Rod! each reply is a great insight

gumside,
if you search SCF for "rust" or "toning"
there is more in-depth conversations.

Also try our "Stampsmarter" database.

Being your focus is Jeruselem issues, I am not surprised at the condition. It is difficult for decent paper storage in hot humid environments. "Tropical toning" is often an issue.

Rod222 I bow to your superior knowledge on gum and deterioration, and also learn from it, but the covers only originated in Palestine, Nottingham,England and Denmark where they were sent to are not in tropical regions. :)

Where they originated from would not give rise to toning (in general)
Gumside, however lives in Israel,
I was considering the items were maybe stored and deteriorated in that region.

Maybe of interest to you.
https://www.academia.edu/34592272

For the original stamp, in the larger image of the front there appear to be dark markings that look like a light cancellation. If so, the stamp may have been steamed off the cover giving rise to the glossy, mirrored appearance.

Many Hong Kong Scott 167 have this appearance. Scott 167 is actually a revenue stamp authorized for use as a postage stamp during a shortage of 5c stamps in Hong Kong. Grifters soon realized that many Scott 167's without cancels could be found on revenue documents. These steamed-off stamps are much more common than truly mint Scott 167's.

As far as the tropicalization, keep in mind that air conditoning was likely unknown in Palestine in the 1920s to 1940s, and there is no way to know how long that particular stamp sat in a drawer, desktop, cubby hole, or brief case. The unknown period of time before the cover was franked could easily be enough time to tropicalize a stamp.