Re: Dag Questions

Brad,

It's good that you have a background in chemistry. Maybe you can invent
some new methods for us!

I buy plates that are purported to have .5mil coatings of silver. In
reality, I'm fairly confident that each plate ranges from .3-.5
depending on where on the plate you look. I'm so uninterested in
complicating my life by plating my own copper that I buy them pre-made.
Dags are complicated enough!

The thickness of the silver is probably most important to the number of
times that you can repolish the plate when you screw up the exposure. I
do this constantly. :( With my plates, I can usually get 2-3 do-overs
before I buff through to the copper beneath. I have a few pieces of
3-nines silver that I intend to polish and use as plates to see the
effects. I'll let you know or otherwise publish in the Daguerreian
society newsletter what I find.

There is a decided advantage to using mercury if you can do so safely!

1. Becquerel dags have a dynamic range of about 2-3 stops whereas
mercury dags have a range of more like 7-9 stops.

2. The exposure time for a bromoiodide-sensitized plate (mercury
method) is far shorter than an iodine-only sensitized plate (Becquerel
method). My Becquerel exposures are in the neighborhood of 4-5 minutes
for zone V at EV 13! With bromoiodide and mercury, you could probably
get the same exposure in 30-40 seconds.

3. Once exposed, a Becquerel plate requires a 2-3 hour development
through a red filter by UV (sun) light. A mercury plate would need to
be exposed to heated mercury vapor for a matter of seconds to minutes
(talk to Mike Robinson or Jerry Spagnoli about this).

Welcome to the club! I highly advise taking a workshop or a one-day
seminar if you can. The Daguerreian society in Rochester offers one-day
workshops periodically. I'm curious to know how you intend to handle
the mercury. What is your setup or recommendation? I have not made
mercury dags yet but I'm anxious to start as soon as I can get a handle
on the safety precautions required.

-Jonathan
http://photographs.danforthsource.com

Bradley Lewis wrote:
> I have a couple questions for the Daguerreotypists out there. I
> really want to get into making my own Dags, but don't think I'll be
> able to attend any workshops on the subject. Fortunately, I am a
> chemist, so a lot of the procedures involved are not too foreign to
> me, hopefully.
>
> First, I was wondering about the thickness of the silver plating on
> the copper. I would like to plate the copper myself. I have read
> somewhere a figure of 0.35 mil or about 10 micrometers. Any idea if
> this is correct, or what range of thicknesses work? Does anyone have
> a feeling for how the thickness of the silver layer affects the image?
>
> Second, I was wondering about the development methods. How do mercury
> developed images differ from Becquerel developed images? I can obtain
> and handle mercury fairly easily, but if there's no real advantage, I
> think I would prefer using the Becquerel method.
>
> I hope I'm not inundating you with questions. Any advise offered
> would be deeply appreciated!
>
> Thanks for your time and assistance in this.
>
> Cheers,
>
> Brad
>
>
>

-- 
http://photographs.danforthsource.com