Re: Mandel's Positive Process

Judy Seigel (jseigel@panix.com)
Fri, 6 Dec 1996 16:46:31 -0500 (EST)

On Sat, 7 Dec 1996, Luis Nadeau wrote:
> Tell them to check Melanograph and Monobath processes in my Encyclopedia
> for a clue. They are fairly common.
>
> I don't have my databases at hand but I am about 99% sure that this was a
> direct reversal print, popular early this century with itinerant
> photographers. It may also refer to the type of camera specifically used
> for it. I'll check tomorrow.
>

I happened to have this on a piece of paper right by the computer, from
"Photographic Amusements," that goldmine of arcania and other photographic
delicacies, p. 90:

Making Direct Positives in the Camera

Prepare a saturated solution in water of the crystals of thiosinamine &
add from 2 to 8 minums of it to an ordinary pyro or eikonogen developer.
Expose rather less than usual. The effect of this addition to the
developing agent is an entire reversal of the image, a positive instead of
a negative being obtained. Ammonia will assist the reversal. Colonel
Waterhouse, the discoverer of this process, recommends in some cases the
plates being subjected to a bath of 5% nitrate [sic] acid and 3%
potassium bichromate before exposure, followed by a thorough washing.

Cheers,

Judy