[alt-photo] Re: pigment problem

[Katharine Thayer]

Hi Julian, well, first a point of clarification about pigment names:  
you're not printing with indigo pigment.  Indigo is PB 66, a pigment  
so fugitive that it is no longer used in any watercolor brands  
(Winsor & Newton was the last to discontinue it, about five years ago  
or so, if I remember right).  All paints named "indigo" nowadays  
aren't actually indigo but are convenience mixes of other pigments,  
mixed in an effort to replicate an indigo hue, and to follow  
traditional naming convention, they should all be named "indigo hue"  
rather than "indigo,"  IMO.  But never mind about that.

While I often mix pigments myself for my own purposes, I try to avoid  
convenience mixtures where I don't have any choice over what pigments  
are used.   I have found some pigment mixtures that produce a split  
tone effect in themselves (I'd have to go back to the archives to be  
reminded of what those were, since I've never gone on to use them in  
my work) in other words one of the pigments in the mix will be more  
evident in the lighter tones and the other pigment in the darker  
tones.  If you're interested in what those pigments were, I'm sure I  
reported it to the list when I made that observation, so it should be  
in the archives somewhere.

What you've got here is phthalo mixed with quinacridone rose,  
apparently to shift the blue more to the red side, plus lamp black to  
darken it.   If it were me and I were looking for an indigo-like hue,  
I would use a single pigment that is close to that hue rather than a  
mixture.  Indanthrone, PB 60, is a very close approximation to indigo.

All that said, I'm not entirely convinced from your description that  
your problem is related to pigment, however; it sounds to me more a  
problem of adhesion, or tooth, in other words that the layer isn't  
attaching to the paper as it should.  It would help to be able to see  
exactly what you're talking about, but if the layer is hardening  
properly but then frilling and lifting off, that's most likely to be  
related to an inadequate "purchase" of the gum layer on the paper.   
So that's the line I would pursue in trying to solve the problem,  
look at issues of sizing, paper, prior layers, to see if there's  
something that is interfering with there being enough tooth left  
available to attach that third layer.

Katharine


On Feb 7, 2011, at 2:33 PM, Julian Smart 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
>
>