[alt-photo] Re: pigment problem

[Peter Friedrichsen]

Julian.

Once upon a time, I had a similar problem to yours. The top layer I 
used contained PB15 (Phthalo blue -green shift) mixed with gum from 
pure pigment and containing no other additives. It was applied over 
two other pigmented layers and it was sloughing off. My paper was 
Fabriano artistico HP  300 gsm with no additional size. I resolved 
the problem by applying this layer first. The cause of the problem 
remains a mystery.

I speculated on causes but that is as far as I got. My speculations were:

1- Phthalo blue has some effect on the surface properties of gum, 
affecting adhesion
2- Phthalo blue particles are extremely small and don't act as anchor 
points unlike pigments with larger particle sizes.
3- Phthalo blue particles are shaped such that they provide no bite 
i.e. anchoring to the previous layer
4?
5?
...

Blue sky speculation....Phthalo blue!

Peter Friedrichsen


At 05:33 PM 02/07/2011, you wrote:
>Hi All,
>
>Maybe one for the pigment experts on the list. I am having a problem 
>printing with Indigo pigment on my gum prints.
>
>I am trying to get a kind of split tone effect on a series of three 
>coat gum prints. My first coat is Burnt Sienna+lampblack (50-50), 
>coat 2 is pure lamp black and the third coat is pure Indigo, which 
>in W+N speak is PBk6,PV19,PB15. The first two coats go on perfectly 
>but the Indigo layer just seems to flake off whatever I try.
>I started the indigo layer with a 1/2 strength Potassium Dichromate 
>(6.5%) solution and kept the exposure the same as the mid-tone 
>second coat (3 minutes in this case), the idea being to only expose 
>the deepest shadows where I wanted the split to occur. The coat 
>started frilling in the still wash within a couple of minutes then 
>just fell off. I then used my stock dichromate  with the exposure 
>constant and the same thing happened.
>
>I have tried the same coats using much thinner concentrations of 
>pigment with much the same result and am now totally baffled as I 
>have never encountered this problem with any other pigment and have 
>used the dilution method for sharpening up shadow detail many times before.
>
>For the record I am using Fabriano Artistico 300gsm HP, 4% gelatine 
>brushed size, formaldehyde hardened, W+N pigments and my exposures 
>are: 1; 4 mins, 2; 3 mins, 3; 3 mins at 13% or 6.5% dichro. dilution.
>
>Any ideas or suggestions would be appreciated,
>
>Julian.
>
>Oh forgot to say I am having trouble seeing my own posts on the 
>list, despite going throught the set-up carefully, which makes 
>communication somewhat difficult......
>_______________________________________________
>Alt-photo-process-list | http://altphotolist.org/listinfo