Re: Back-exposing on plastic (was: Re: Gum transfer

Katharine & all,

just a thought on making back exposure gum prints maybe the negative as to
be fitted with a curve since you have no other control now (multi-exposure,
long exp, short exp, pigment load, etc). Maybe this would make a world of
difference...

Regards
Yves

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, April 27, 2006 12:14 PM
Subject: Re: Back-exposing on plastic (was: Re: Gum transfer

>
> On Apr 26, 2006, at 2:56 PM, Marek Matusz wrote:
>
> > Katharine,
> > It is always good to look at actual prints, though imperfect they
> > might be. Thanks for posting your work. I think that you can easily
> > see a big difference of back vs. front exposure.
>
> Of course, I can see a big difference between back vs front
> exposure on the plastic, just as I saw and reported with the earlier
> comparison I showed using ivory black, but the point here was that so
> far I haven't seen anything in my own experiments that looks better
> than I could do with a one-coat (front-exposed) on paper. I was
> looking for more tonal delicacy, as Peter put it earlier.
>
> > Although the recipes and practice might be far from perfect it is
> > this first observation that leads to a new discovery.
>
> Yes, I agree, and I think that's what happened before: my initial
> experiment led to your more interesting results.
>
>
> > To clarify my recipe, my gum mix consisted of 0.25 g of dry lamp
> > black from Daniel Smith (or is it called carnbon black?, can't
> > remember at this moment),
>
> Obviously there's no way to compare this to the amount of paint I'm
> using, as we don't know how much pigment is in a given amount of a
> given brand of a paint made of a given pigment.
>
> > 3 grams of dry gum (I actually used 10cc of 14 baume gum which is
> > about 30%)
>
> By the same (or a similar) token I can't tell how much actual gum was
> in the emulsion, because I start with an amount of pigment-gum mix
> rather than with a given amount of premixed gum, to which a given
> amount of pigment is added. I know that the pigment-gum mix stock
> solution I'm using was made from 15 ml premixed gum and 5 grams of
> paint, and I know that I'm using 2.5 ml of that mix. But another
> wrinkle is that the paint contains gum arabic as well, and there's no
> way of knowing how much.
>
> > and 0.6 grams of ammonium dichromate (2 cc of 30% solution), all in
> > 12 cc of solution.
>
> I used .135 g dichromate (.5 ml of 27% solution) in 3 cc total
> emulsion. For the first one (#3) I used .675 g dichromate (2.5 ml of
> 27% solution) in 5 cc total emulsion.
>
>
>
> > The total volume of the solution is incidental as it only serves to
> > dissolve everything and make the solution spreadable. Once the gum
> > dries, it is the weight of dry components that will determine final
> > properties of the mixture.
>
> Seems plausible in theory, but given my own observations over time I
> wonder if this is so. I might have to drop my cleaning and sorting
> and try mixing a different dichromate solution to see if less
> dichromate in the same amount of water has the same effect. If so,
> then I'd have to agree that the reduced DMax in #3 is caused by
> something other than more water in the emulsion.
>
> It seems like anyone who wants to investigate this effect seriously
> should do as Marek is doing; use powdered pigment. I'm not sure my
> initial results have excited me enough to get that serious about it,
> but maybe after I get moved and set up again. But one thing this has
> definitely taught me, is that if one is going to print on plastic,
> one should definitely print from the back.
>
> Katharine
>
Received on Thu Apr 27 11:35:37 2006