joints dans le prolongement de la tige

21:55 May 26, 2017 

Yes, TonyM, thank you, I think you're understanding my dilemma.
The problem is I can't upload the plate. The text seems to indicate that the extension was added and brazed, which I would think could create joints.
https://babel.hathitrust.org/cgi/pt?id=gri.ark:/13960/t3fx9n... for all it's worth. But there's nothing under or above the mount that seems to be helpful. The plate cuts off just below the capital and horns/monture. No sign of a tang or stem or handle can be seen!

20:46 May 26, 2017 

Not quite, I don't think! I believe you may be parsing it incorrectly, which is leading you astray. My reading would be:

"...on y constate des joints dans le prolongement de la tige, non complètement effacés par le travail du polissage ..."

I don't think 'dans le prolongement' means 'in line with'; I am not clear as to quite what exactly it DOES mean, but it sounds on the face of it as if this is the 'extension' to the tang you talk about — could the extension itself possibly be made up of more than one piece, so it would have joints within it? Unless they mean the one join between the tang and the extension; but that seems at odds with what is actually written, particularly the plural of 'joints'. Are you sure this is actually a 'tang' here? I'm beginning to wonder if this isn't actually literally the stem or handle, which would explain why it needed to be extended? I also wonder why the author suddenly starts talking about examining the 'faces' (which one assumes would be of the mirror itself) and spotting the joints in the stem? Is it in fact the faces of a non-cylindrical stem?

20:08 May 26, 2017 

La partie de la tige ainsi engagée est longue de 26 millimètres. Pas de trou de rivet dans la tige.
This concludes the Technique section.