[alt-photo] Re: Nature of Curtis Orotones WAS Re: wet-plate collodion

[etienne garbaux]

Jeremy wrote:

>I have never heard of them being
>Ambrotypes (positive wet plate collodion on glass).

To be technical (perhaps overly so), ambrotypes aren't really 
"positive wet plate collodion" images, at least as that term is 
normally used.  Viewed by transmitted light, they are more or less 
normal-looking negatives, with more silver in the highlight areas and 
less in the shadow areas.  They appear positive for the same reason a 
daguerrotype and a tintype do -- because one develolps the silver to 
look whitish or grey rather than black, and then looks at them by 
reflected light with something dark behind them (in the case of 
daguerrotypes, the dark is actually in front (typically, the velvet 
lining of the case), and you are viewing it in the mirror of the 
polished plate where no (or little) image silver was deposited.  So 
they look lighter where there is more silver and darker where there 
is less.  You can get the same effect (to a lesser degree) with an 
ordinary B/W negative if you hold it with something dark behind it 
and catch the relected light just right.

Brest regards,

etienne