Re: Dry Plate Speed & Shelflife

----- Original Message -----
From: "Robert Newcomb" <newcombr@uga.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, March 01, 2005 8:53 AM
Subject: Dry Plate Speed & Shelflife

> I've been interested in making my own glass dry-plates to
> shoot in camera - I like some of the "errors" introduced
> from hand poured emulsions.
> A couple of questions for all you knowledgeable people out
> there.
> 1) I have read that the speed of early dry-plates was
> about 7 stops slower then the wet -plate process in use at
> the time. While I'm certainly not trying to shoot action
> sports shots, we're talking Very slow here. I have heard
> that the bottled silver emulsions have an in camera speed
> of about ISO 1/2- maybe 1.
> Is their a component (bromide?) or procedure that will
> make a hand poured dry plate at least as fast as wet
> plates?
> 2) I have also understood that early dry plates (hand
> poured) had a useful shelf-life of only a few days or a
> week after being made in which one must expose them. Is
> their a means of extending this shelf-life to a couple of
> weeks or at least something more the a few days? I'd hate
> to make them and then not be able to go out shooting the
> next day so the plate spoil.
> I understand that commercially prepared plates later
> overcame these factors but what is possible of the home
> brewer?
>
> Thank you,
> Robert Newcomb
>
   There are some interesting comments in the book _From Dry
Plates to Ektachrome Film_ C.E.K. Mees, et.al. Mees was head
of Kodak's research laboratory from its inception in 1912
until his retirement in 1960. The book is a kind of memoir.
Mees was initially a partner in Wratten and Wainwright.
George Eastman bought W&W to get Mees. Mees talks about
Wratten's early dry plates and states that the speed of
plates from c.1880 was on the order of 40 times that of wet
plates. He also states that wet plates had rather uniform
speed so early dry plates were often rated in the
comparitive exposure to wet plates. (see chapter 2)
  Mees also remarks that Wratten dry plates had good keeping
qualities which made them popular for export use expecially
to tropical areas. The early plates were hand coated using
tea pots to hold the emulsion for pouring. While he does not
go into detail this does suggest that early dry plates could
have reasonably good keeping qualities even before machine
coating. W&W was also an early supplier of panchromatic
plates.
   This is a non-technical book where there is often a
blurring of dates but the above seems to be reasonably
clear.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com