A seam allows you to take a flat piece of leather and stitch it into a shape the somewhat resembles the shoe, a little bit of stretching and shaping is still required to get proper fit on the last but it should be within the leathers natural stretch limits.
A seemless wholecut has no seems so you have to stretch the leather tremendously especially around the heel and ankle area, so much so that sometimes it is past the leathers tensile limits or always very close to it
I have tried this...successfully...and in my somewhat limited experience with this specific style I would have to say that your remarks are not quite correct or...perhaps, better...not quite complete.
Generally speaking, the problem is too much leather. So that you must have some way of eliminating the excess. Some leathers...veg tans...will form to a shape fairly easily and some (not all) of the excess can be subsumed in the shape. Functionally, this means compressing pipes and wrinkles to the point where they are not visible.
Other leathers (chrome tans) must be stretched to remove excess. It's the only way. And in such circumstances such leathers may be overworked, it's true. And as a result softer tannages are often used--which in turn don't have the strength that firmer leathers have.
When I did this, the leather I used was a retan ( a tannage of both chrome and vegetable). I had more problems with excess than I might have if the leather had been full veg, but less than with a chrome. As it was, I never felt that I had over-stretched the leather but the excess was very slightly visible. Since the leather was naturally "textured", it was almost impossible to see this if you were not a shoemaker or had a great deal of experience.
Anyway, the point is that while the style presents problems, they don't necessarily have to affect either the integrity of the leather nor the customer's satisfaction.
First off, for anyone following this part know that DWFII is the expert here.
This is interesting and good to know. I was not aware that veg tan would as you say "subsume" to this level . Does this cause the leather to thicken substantially in such areas? My train of thought was definitely on chrome tannage and I assumed the throat area and surrounding would have been cut with a much smaller circumferance than last in order to avoid the large excess below.
When doing this do you wet the veg tan upper completely, not at all...? I have little knowledge of chrome-veg retans, are the characteristics almost always somewhere in between veg and chrome, or do they sometimes behave strictly like one or the other.
BTW who do you use for veg and veg retan uppers? have you tried Weinheimer's?
Well, thank you for the kind words but no, I'm not an expert esp. with seamless whole cuts. That said, I know enough about leathers, and making shoes and patterns for shoes, that I was successful doing this the first time out of the gate...never a sure thing.
Fundamentally, the upper is cut as an overlarge "blocker"--just a big flat piece of leather--and then it is wet thoroughly and stretched over the last from the top of the last towards the bottom. From the forepart to the instep it is pretty straight-forward...like lasting a shoe. But from the instep back to the heel all the excess must be moved along a vertical surface. And this is the longest distance that the leather must be moved.
Naturally, forcing pipes and wrinkles into smaller and smaller dimensions tends to thicken the leather...if stretch is not also applied simultaneously. But around the throat--the topline--there shouldn't be any significant excess left nor any real over-stretching.
Only after the leather has been stretched over the last is the pattern cut.
The bad news is that even if the pipes and wrinkles are entirely subsumed not all of the excess is eliminated...some of it remains in the leather. The good news is that much of it will be positioned over the heel stiffener and will be reinforced. Plus, the heel area does not get a lot of stretching or flexing when the shoe is worn.
I do not know of Weinheimers but very few tanners make veg tan leathers that are finished and suitable for shoe uppers...and almost none of those tanners are in the States. I get pure veg where and when I can and veg retans as water buffalo calf from an outfit in New Hampshire (?)--Garlin Leathers.
In a series of articles in The Rake Online, Simon Crompton shows pics of some seamless loafers that G&G have underway for him. If you see part 4 (5/3/2012) and click through to the full article, you can a number of pictures of the upper being stretched over the last, and the amount of leather that has to be dealt with, particularly around the heel. Even in the upper they show after the stretching is done, you can see some 'pipes' on the outside of the shoe in the quarter area.
The leather is fully wetted before it is stretched over the last; when wet, veg tan becomes much more pliable. Furthermore, as it dries it tends to shrink a bit -- a good think when you are trying to get it tight to the last --, and when fully dried it tends to hold its new shape.
DW -- I think you are referring to Garlin-Neumann Leather