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

RE: Gum over Cyanotypes

On Wed, 29 Apr 2009, Don Bryant wrote:


I used to but don't any longer. Judy Seigel has a great write up in The Post
Factory Journal that describes a method for tray sizing. Get a copy if you

Don Bryant
Thanks for the plug Don, I was afraid to mention that for fear of being accused of *commercialism* (it has happened, tho that's another story for another day). But what I REALLY want to say is that if you guys aren't vat sizing and your size coats are OK, you are leading a charmed life.

In my experience (and every once in a while I need or think I need to re-size in the middle of a print, and do it by brush -- or foam pad), a brush size is absolutely not not NOT the same, and the troubles mentioned can very well be due to that (and even if they're not, they are).

In any event, my experience -- and belief -- are that a vat size permeates the paper, right into its heart, not merely a surface coat that can wash off or abrade, and it seems to me that given some of the lengths to which folks go (like omigod, "measuring UV absorbence of a narrow spectral region that varies as the amount of ink varies" that makes my eyes cross) to NOT vat size is like straining at a gnat & swallowing a camel (to not coin a phrase).

There are two possible problems with vat sizing: as mentioned above, the gelatin can get cool: All the problems in your life should be so easily solved: You simply fill a LARGER tray with hot water, and set the gelatin tray in it. It helps to have an immersion thermometer, but you'd want that anyway, because the ideal temperature for the gelatin can be monitored.

I'd say that you want it above 120 degrees F, and below 140 degrees, as hotter than that can degrade the gelatin.

And you do need a helluva lot of gelatin-- tho everything you use should be as cheap as Knox unflavored, which my tests showed to be the best. I'll quote here my instructions (in P-F #1) for measuring that:

"Fill a tray large enough to hold the paper without bending it with enough gelatin to cover a stack can take 4 or more litres. To estimate volume before mixing, fill the tray with water to the desired depth (one to two inches?), measuring as you go. Large quantities can be sized in two or more batches.

Pour about a third of the water into a pot and sprinkle the dry gelatin over it: stir without shaking, just until it's all wet, then let soak, 15 to 20 minutes. Add remaining water, stirring slowly, gently, to avoid bubbles, and heat over a low flame while stirring, until gelatin is nearly 140 degrees F. (60 C.), but not hotter."

Then I describe devices to keep the bath hot, if the room is cold: aquarium heaters, water-bed heaters, color-printing heaters, immersion coils... etc. but "it helps, if the room is really cold, to make the gelatin 3/4 strength, so it doesn't set quite so quickly. (I've done that with no noticeable ill effects.)

"Slip the paper one sheet at a time, into the gelatin solution, turning once to check for airbells which you brush or wipe off.... After some 10 minutes, turn the stack over and remove the paper, first in, first out...etc."

This issue describes giving the paper a gentle squeegee with plastic rod against tray rim to remove excess gelatin when you take it out, but I devised a better way described in (I think it was) P-F #9. That is. you stand a sheet of glass up in the tray, at an angle against a wall, and put one sheet at a time on the glass, face down... and gently squeegee the back with a soft rubber squeegee. Then hang to dry. There's a diagram showing that, but the idea is simple enough -- and it saves the risk of drips, and sized paper sticking to another sheet as you lift or carry them.

Then you harden...Etc. etc. etc, and so on for pages... but when you think of the time, talent, heart and money you'll spend on those prints, the extra trouble of vat sizing is as nothing.

And now -- oops, I could have saved the 20 minutes this took me -- P-F #1 is on Malin's website, Alternativephotography.com (there's a more detailed address but I can't find it now -- maybe someone knows it?) and you can download it as a pdf and print it out for free...