8 Reales Zs 1835 ... 25.59 Gr ?

The angle of the photo is ok. The edge has a slope.
Imho the angle of the slope depends on the thickness of the blank at this area. The coin in the area of this slope is thiner by 0.2-0.3 mm than the opposite part of the coin. Maybe this affected the edger to tilt.

The slope seen in the final picture is seen on a good many original coins from the 1834-1836 time frame at Zacatecas and was caused by worn "cookie cutter" blanking punch in the blanking room. A dull (worn) cutter does NOT make a square cut through the silver stock but rather tends to tear through the metal and results in many sprues and in this case a sloped edge. The edging operation often rolls the torn edge into a fold or simply a slope as seen here.

This is normal and seen during periods when the apparatus was in bad need of replacement.

The "appearance" of the segments being at an angle to the faces of the coin is as I said earlier mostly an optical illusion due to the fact that they are located on the surface curving away from view. The detail actually remains square to the faces of the coin but follows the sloped edge of the planchet. The edge mill did this when wear allowed for some "travel" or play in the dies.

Do not worry about it being a forgery in this particular case - that appearance is quite normal.

It is possible that the cutter could have produced the lines seen on the edge of that coin. It is also possible that it represents the edge of the rolled sheet.

The sheets of rolled silver used in the days of hand powered rollers were just over one blank in diameter and blanks were punched one at a time. If the width of the sheet did not allow for a full punch - the workman often made the blank anyway to see if it met standards. Payment was based on the number of units completed so they would have made the punch and if it was rejected it represented little extra work comparatively.

The "debased" issues were die struck - that is an established fact. They are not castings made from casts of original coins. The fact that they use "real" mint design dies is the major issue and reason behind the question of who made them and were. Were they made in the mint or outside? Were real mint dies or punches used? These are the two primary questions.

There are two nearly equally plausible theories of where these debased strikes came from. The first is that debased planchets or blanks were substituted for real examples in the mint. The second is that old dies were sold as scrap without being defaced.

The second cause is well documented in period sources as actually occurring. The first is alluded to as well. So in either event which is the actual source is uncertain in the contemporary record. But both may have taken place.

My belief is that the worn die theory is far more plausible unless the deception had support at the level of the assayer and refiner at the least. Substitution of a planchet or blank from outside the mint is less likely than corruption of the officials because the silver and the resulting blanks were accounted for at every step.

So I do believe that most of the "matching" die debased coins were made outside the mint using scrap dies. They can be identified in some cases by the edger used, but I am also certain that some debased examples using the correct edge design and methods of application do exist so an origin in the mint is possible as well.

The problem with these particular years are that there were so many dies used that a match would be pure luck.

The edges lead me to believe that some were made outside the mint because the edges are AWFUL. But others do have better edges. None of the dies are near terminal state (at least the ones I own).

It is definitely an are that needs much more study than I have time for right now.