The Daguerreotype is a copper plate that is silver plated and polished to a
mirror finish.
The plate upon being vaporized with iodine is rendered light sensitive as
the silver is now silver iodide and bromide. When exposed after an
extremely long period it is then fumed with mercury. Where the plate was
most exposed (the highlights) a mercury silver amalgam is formed. Creating
the highlights.
The plate is then processed in potassium cyanide or sodium hyposulphite.
The unacted-upon iodide and bromide are disolved away via this fixing
process.
The actual shadow areas are the inabillity of the mirrored surface to
reflect darkness. The daggureotype must be viewed in such a way that the
shadow areas reflect no light. Thus contrasting the mercury silver
amalgam..
I hope I worded this so it makes sense.
Sincerely,
Jonathan
----- Original Message -----
From: "ken" <watsok@frii.com>
To: <alt-photo-process-l@skyway.usask.ca>
Sent: Friday, December 10, 1999 12:06 AM
Subject: RE: Daguerrotype reverse?
> One of the things they were doing, at the time, was placing a silvered
prism
> in front of the lens. By taking a picture through the prism the image was
> correct on the Dag. Exposure was not affected.
>
> -----Original Message-----
> From: SCHRAMMR@WLSVAX.WVNET.EDU [mailto:SCHRAMMR@WLSVAX.WVNET.EDU]
> Sent: Thursday, December 09, 1999 8:00 PM
> To: alt-photo-process-l@skyway.usask.ca
> Subject: Re: Daguerrotype development
>
>
> Let me try to answer this. Before exposure the daguerreotype plate is
coated
> evenly with silver halides. When light hits the plate the silver halides
are
> reduced to metallic silver in the highlights. Ordinary gel/silver
developer
> would simply hasten this process. In the shadows, silver halides would be
> covering the metallic silver plate. During fixing all the silver hallides
> would be removed thus you would have an image formed out of metallic
silver
> surrounded by metallic silver. Ergo, no image visable.
>
> What I believe happens in mercury development is that the mercury
condenses
> on the plate in the region where the silver halogens have been reduced
> by the action of light to metallic silver where they amalgamate(sp?) with
> the
> metallic silver. This does not happen in the shadow areas because they are
> covered with AgI and AgBr at the time of development. After development
> the remaining silver hallides are converted into water soluable compounds
by
> the sodium thiosulfate and washed away revealing the silver surface which
> appears dark while the little mercury drops appear light.
>
> It is the optics that reverses the image. You are looking at the original.
>
> In modern positive/negative photography the image is reversed again during
> printing. Remember, you print with the "shiney side" up which is not the
> emulsion side.
>
> Bob Schramm
>
This archive was generated by hypermail 2b29 : Tue Jan 11 2000 - 12:10:48