Improperly Mixed Pigment?

Is this possibly a gathering of unmixed pigment or retention agent?

It would really help put this in context to show us the entire item. We have ZERO idea what you are showing, whether new or old or ?

Please, show a full view of the object so it can be put into perspective.
This looks like a heavily enlarged minute spot in a piece of paper.

And what is on the front?

Exactly

Thanks Rogdcam.

Beyond the normal pulp-processing chemicals, the papermaking process can have various contaminants introduced through the raw materials and the processing steps.
Depending on the era and pulp recipe, what contaminants can come in with recycled rag stock or aren't eliminated by imperfectly-processed wood pulp?
Although not written prominently in the philatelic literature, consider bits of undigested straw in some of the U.S. banknote era "straw paper" printings.
The papermaking process can also have all sorts of intentional additives such as fillers and coatings to improve the performance of the end product as well as intentional additives used for security purposes such as colored silk fibers of varying lengths, colorants, etc.
The stamp in question here has numerous small bits included in the pulp, as noted in yellow. Are they intentional or contaminants? The last paper comment I see in Scott is with France #104 as "ordinary paper", which apparently continues from there onward.

Without a true chemical analysis by a paper expert, it seems best to call it a "stamp with small inclusion on reverse" and not attribute it to anything specific, although most collectors would likely ignore it since it is not visible on the front.

Just_fella: Where are you getting the detailed suggestion/idea that this is an unmixed pigment or retention agent?
Rogdcam: What leads you to agree with the unmixed pigment or retention agent idea?

I do not suggest all this flipantly, as I have degrees in chemistry and packaging, which means I have dealt in no small amount with paper, beyond the experiences in the philatelic world.

Also how a single small spot appears on only that position of the stamp that, once, was attached to something, remains unclear.

It, likely, is another one of those things where OP sees zebra stripes and will try to convince everyone a platypus is sleeping in the middle of the road.

Zebra and platypus?
What does that have to do with stamps?

NSK answered for me in a nicer way than I ever could have:




It was a flippant non-answer meant to signal nothing and I should have not entered a word and moved on from this topic. I let emotions from previous experiences rise to the top. Not proud of that.

I don't think that the tiny spot is anything other than either a paper remnant from the cover the stamp was soaked from or an inclusion. Ordinarily such a speck would not merit a second glance but in this case it could go on ad nauseam.

PS: I have no clue what a "retention agent" is nor am I going to Google it.

I'm hoping that this thread doesn't evolve into the OP or others claiming to see some sort of pattern in those highlighted specs. We've been there before, and it didn't end well.

Might be from the bandes publicitaires listings in Maury?

Told you so.