Re: Self-toning Gelatin P.O.P.

Date view Thread view Subject view Author view

From: Liam Lawless (lawless@ic24.net)
Date: 04/24/00-12:51:09 PM Z

Sil,

A note from Southworth & Bentley:

LEAD ACETATE (Plumbic acetate, sugar of lead), Pb(CH3COO)2.3H2O = 379
Coarse efflorescent crystals with faint odour of acetic acid. Highly
poisonous (antidotes: white of egg, magnesia or sodium sulphate). Dissolves
in water, generally giving a cloudy solution. This cloudiness may be
removed, except with permanently-hard water, by the addition of a few drops
of acetic acid. Must not be treated with hot water. Stable both as solid
and in solution. Has a limited application in combined toning and fixing
baths for gelatino-chloride papers, the toning action being produced by the
formation of lead sulphide. For this purpose the well-crystallized, pure
white product, completely soluble in distilled water, is needed; may be kept
in ordinary corked bottles.

Liam

-----Original Message-----
From: Sil Horwitz <silh@earthlink.net>
To: alt-photo-process-l@sask.usask.ca <alt-photo-process-l@sask.usask.ca>
Date: 23 April 2000 04:17
Subject: Re: Self-toning Gelatin P.O.P.

>At 2000/04/23 03:10 AM +0100, Liam wrote:
>
>>B. Ammonium sulphocyanide . 2 oz.
>> Water to make . . 8.25 oz.
>>C. Lead acetate . 1 oz.
>> Boiling water to make .8.25 oz.
>>
>>A dense precipitate will settle. The bottle mast be well shaken each time
>>any solution is required.
>
>Wow! Lead acetate is very toxic, even in small quantities. In addition,
>lead thiocyanate (old name: lead sulphocyanide) is about as insoluble a
>compound as you can make, so that's what the precipitate will be, and of no
>use whatsoever. Can't imagine what the purpose is, as lead is a gold killer
>- why would you want to inhibit the toning and waste gold? There are more
>modern, better formulas. In fact, in my experience it is better to do the
>gold toning after a quick wash and prior to fixation and final wash.
>
>Just curious: anyone reading this know specifically what the purpose of
>precipitated lead thiocyanate is in this formula? You couldn't dispose of
>this down the drain, either, what with all the restrictions on lead
disposal!
>
>
>Sil Horwitz, FPSA
>Technical Editor, PSA Journal
>teched@psa-photo.org
>silh@earthlink.net
>Visit http://www.psa-photo.org/
>Personal page: http://home.earthlink.net/~silh/

Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : 06/13/00-03:09:49 PM Z CST