rockland colloid sells a tintype kit that reverses the negative.
its for making silver gelatin tintypes as well as silver gelatin glas ( like ambrotypes)
it uses a proprietary developer which is like a weak bath of dektol, fixer and thiocyanate bleach
but its trickier than that ... there are a handful of threads here on apug about this finicky process.
ive made a handful of these tin and glass images and i am currently trying to concoct my own revesal developer.
street photographers in around 1900-ww1 used this process, but unfortunately very few
of the developer recipes have surfaced.