[alt-photo] pigment problem

[Julian Smart]

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......