[Alt-photo] Re: casein on glass

[Matti Koskinen]

Dear Jorj,

zillion thanks for the info, really appreciated. I tried to clean the glass panes, but hardened and dried casein sits on the glass: I tried different solvents, none had any effect, then just used very fine steel wool to scrub the glass.

I used to do negs with different inkjet printers, but then I just tried the smooth side of an OHP-transparency, which is made for laser printers, other side for inkjet, and the neg was very smooth, much smoother than creating error-diffusion bitmap with PS, which I used before when printing photos with laser. The HP-driver for a second-hand HP Laserjet 1018, gives really smooth, to my eyes dot-free prints. Sometimes the negs have lines on them, but printing again, I normally get a useful neg. And lasers are fast compared to inkjets.

The curve is really interesting, once ChartThrob made quite alike a curve for cyano.

I wrote a program long ago, which takes the original image, a reference image and tries to adjust histogram of the original to be like the histogram of the reference image. Didn't think too much, but the basic idea was, that if you have good image after the curve applied, you could use this for another image to adjust it ready for neg. Your psd, which has both the original full-tone version and curve for it, made me think this code again. I'll check with some images, probably not good for adjusting them, but interesting to see.

I've been using acrylic paint or gouache. Yesterday couldn't find my gouache, so I used process black acrylic, and it worked very well.

thanks again.

-matti







On May 30, 2013, at 3:06 PM, Jorj Bauer <jorj at jorj.org> wrote:

>> now it's the immense task to find the proper PS-curve, On Jalo's book, there's one picture of tens of ChartThrob prints hanging drying.
> 
> I know the feeling. I've got piles of them too.
> 
> Maybe this will help you: I dug up my notes for She Drank a Little Whiskey.
> 
> The glass is prepped with a scrub of barkeeper's friend (later prints had very little to no glass prep; I found it unnecessary, except to remove the tape residue from its packaging).
> 
> I'm printing the negs with epson inks on a Stylus Pro 4000, and I found that cyan is particularly good at blocking the right UV wavelength for casein prints, so there's an overlay of RGB 88/76/00. The negatives are also printed with a border; trimming them to that border yields a neg that lines up with the edges of the glass. That's how I register on glass; to the edges of the pane. Of course since I'm printing on multiple panes of glass, I then register the panes with each other when they're set in the final frame.
> 
> I put a scaled-down version of the photoshop document here, which might be useful to see what I meant by all of that:
> 
> 	http://www.jorj.org/expire/whiskey-negs.psd
> 
> and just the curve, which I also use for 5 minute casein exposures on Fabriano Artistico, here:
> 
> 	http://www.jorj.org/expire/jorj_887600_casein_5m_fabart.acv
> 
> 
> I used Schmincke pigments, ~0.3g, with 3ml of 10% ammonium caseinate and 3ml of ~13% (saturated) potassium dichromate, reheated to get it back in solution (the ambient temperature was probably 50F/10C). That covered two 8x10 panes of glass; I like to print at least two at once.
> 
> I noted that 0.5g of pigment was too much and caused flaking while soaking in water.
> 
> Potassium dichromate was an important part of the process. I noted a lot of failures using ammonium dichromate. I'm sure one could make AmDi work just fine with enough work. I didn't put in too much effort.
> 
> My casein stock is dry casein powder, used for milk paints. It's much easier to work with than milk, and stores a lot better :) 500g of "Ultra Casein Powder" from earthpigments.com, looks to be a 5-year supply for me.
> 
> Brushed 3ml on to an 8"x10" pane of glass, edge-to-edge, over a 5-minute period. Not brushed continuously; I let it rest for ~30 seconds between brushings at first, and gave it more regular brushings as it approached dry (over about 10 minutes). Dried ~30 minutes longer in a drying cabinet.
> 
> Exposures are between 6 and 7.5 minutes; it looks like my starting point was 7.5, and some layers/negatives pushed me down as low as 6. (Homemade UV BL exposure unit, about 6" away from the vacuum frame.)
> 
> The casein stuck firmly to the sheets of glass, which cleared in about 90 seconds of cold water soak.
> 
> 
> -- Jorj
> 
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