[alt-photo] Re: Gum over cyanotype question

[Christina Anderson]

Matt,
I haven't read all the answers yet, so forgive me if this has been answered; trying to clean out my inbox.

Burnt sienna for me takes a LONG exposure. 15 minutes is even not too long. I don't know why this is the case--whether an earth pigment is more opaque to light or not, but I find that yellow, burnt sienna, and black expose from longer to longest in that order, and though I choose a standard printing time around 6 minutes, thalo is happy with 4 or 5, magenta 5 or 6, yellow 9, burnt sienna a sort of whoops I left it in the UVBL longer so what, and black 9-15 as well. I know this sounds really loose and unscientific, but I am just not so rigorous when my timer goes off to get back into the dimroom and remove the contact frame from the UVBL unit. But I will say that actually I have tested all colors with a step wedge and found this to be true as well.

It is hard to be exact about this because I find that gum can expose at all kinds of minutes/choices. I use a 6 minute ballpark because it provides a layer that is very stable in development and will allow some spray development in the beginning five or ten minutes. 

I use 15% ammonium dichromate 1:1 with gum/pigment.

I have never had the cyanotype layer determine whether or not the gum sloughs off or not.

Any part of the cyanotype that is covered by a gum layer does not wash out for me.

NO tween in the gum layer.

Slickness and sloughing off in my experience is more determined by too thick a layer of gum, not enough exposure, too much sizing.

Hope at least one of these points helps.

Chris

Christina Z. Anderson
christinaZanderson.com

On Feb 27, 2012, at 8:52 AM, Willen, Matthew S wrote:

> Hi All,
> I am working on some duotone prints using a cyanotype layer on the bottom and gum layer of an umber or sienna over the top. I'm using a stock solution of cyanotype from B/S. A couple of things happen: 1) I find that the gum layer doesn't stick particularly well to the cyanotype, it almost peels off; and 2) even though I wash throughly and all the cyanotype layer to dry well, I lose a lot of the density of that layer in the extended gum wash. Any suggestions? Perhaps some tween in the gum layer? I've also developed the cyanotype in a Hydrogen peroxide/H20 solution. Might that make it more slick? Thanks.
> 
> Matt
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