U of S | Mailing List Archive | alt-photo-process-l | Re: Gum over Cyanotypes

Re: Gum over Cyanotypes

Hi Don
Contributors to earlier threads on the subject of neutralising the buffer have discussed various acid alternatives.   Ryuji Suzuki has suggested it is better to use a chelating agent.  It appears that any acid will attack paper fibres - here is an interesting explanation from a commercial site:
Do you print your cyanotypes over glutaraldehyde-hardened gelatine?  If so, I wonder whether the gelatine would act as a barrier (so with a bit of luck the cyanotypes would never know there is calcium carbonate lurking back there in the paper fibres).
Don Sweet
----- Original Message -----
From: Don Bryant
Sent: Wednesday, April 29, 2009 1:05 PM
Subject: RE: Gum over Cyanotypes



Well here is my method for pre-shrinking FAEW or FAT.


First I pre-shrink parent sized sheets 10 at a time in our garden sized bath tube for several hours with luke warm water. Initially each sheet is immersed and allowed to become saturated with water. After all of the 10 sheets are in the tube I will inter-leave the sheets slowly over a period of several hours. I handle the sheets with care to prevent scuffing of the paper surface. After 5 or 6 hours (by that time the water is cold). Iíll pull the sheets and hang to dry completely. After the sheets are dry I will repeat the process. Over a period of days I will pre-shrink a batch of 100 sheets.


After the second pre-shrink cycle I size the sheets with gelatin hardened with glutaraldehyde. Those are hung to dry and after drying are stacked carefully in one of the drawers of my flat file cabinet. The stack is weighted to help flatten the stack.


I print cyanotype on the sized paper and never have a problem doing so. Printing the cyanotype on the sized paper makes for a sharper image, IMO. I register negatives by eye for gum exposures by laying the coated sheet on a light box with a sheet of glass lying on top of the negative. The negative is taped in place once the registration is achieved and then exposed to UV. I never have any problem registering negs 11x14 or smaller.


For gum over palladium I acidify the paper in Oxalic acid (5% for 20 minutes) though I donít do this with parent sized sheets. Iíve never had a problem with the so called calcium carbonate deposits coating the paper surface after the oxaclic acid bath. I also have concerns about using an inorganic acid such as HCL affecting the archival qualities of the paper, even a dilute solution.


After the palladium layer has been printed then I size the paper with gelatin hardened with glut. I have done as many as 5 to 6 gum layers, though typically itís 3 or 4 gum layers with different dichromate dilutions with different pigment colors. Iím not much into gum over cyanotype unless I do tri-color. I never have a problem with staining, my prints look sharp.


So, there is more than one way to skin the gum cat. I am concerned about the pH of the paper after clearing in sodium metaborate as a result I wash the prints well. I have a high chlorine content to my tap water so Iím sure my prints arenít pH neutral after the wash. But I soilder on never the less.


Don Bryant