U of S | Mailing List Archive | alt-photo-process-l | Re: tips for using dry pigment

Re: tips for using dry pigment

hello judy.
i got the P-F issues on friday (that was rather quick). thanks! i've been reading like mad since then.

sugar: i need the sugar to keep the curl out of the carbon tissue. i can't go below 60gr/liter. i've tried 40 and it was too little. one time i completely forgot the sugar and the result was a tissue that was almost unusable because of the curl.
i've read carbon formulas that called for a lot of strange stuff, honey one among them. i got the forumla with sugar from the sandy king article on unblinkingeye. i think the sugar is not supposed to do anything image-wise, but only keep the tissue flat.

whoops. i used the wrong word, "brick and mortar" for "pestle and mortar". of course i was not grinding it with a brick. i do use "grinding" to mix the pigment with the fluid, not to grind the pigment finer. i read a little about how it's done in painting and they all used a thing like a mortar and pestle to mix it.
i don't have problems mixing for gum, it's fine after just a little mixing with the brush. carbon is different, it's a lot more pigment (7gr for 500ml pigmented gelatin solution). when i put the water into the mortar, the pigment floats on top at first, then goes into the solution while mixing. i thought about adding a dash of alcohol to get rid of the surface tension of the water. it would make the process easier and less messy at the beginning.

i have to pre-mix the pigment in a little bit of fluid before adding it to the whole batch; mixing it in the 500ml of gelatin would be very messy and impractical. so i just mix it in a little bit of water, then add it to the whole.

i still haven't got a stouffer-step wedge, but i just prepared some carbon tissue to do the same testing with chart throb (digital step wedge and analysis program), i just did with gum printing. so, soon i'll be able to say more about that.
(i could post the scans of my comparsion of 5% vr saturated ammonium dichromate, if interesting to someone and not a complete bore fest. saturated is highly superior, step-wise. but i might try and use 5% for my shadow exposures)

phritz




Judy Seigel schrieb:

Phritz, I don't suggest adding so much as subtracting. Have you done a variables test without the sugar? I found that it not only didn't improve, it disimproved... But you don't say how you're judging results. Have you got a 21-step or other measured density transparency? Have you tested this mix against anything else?

For what it's worth, unless you're digging your own dry pigment out of your own hole in the ground, it comes from the store as fine as you can possibly use, which is to say, more finely ground than you could improve on if you "ground" it for the next millenium.

I got this directly from founder of Golden pigments years ago at a College Art Association conference. The reason you "grind" is to be sure you've got every particle surrounded by gum arabic (or linseed oil if you're doing oil paint, etc.) so it won't clump when you add the other ingredients.

That sugar business is pure nonsense, somebody's bright idea after sucking up too many lollipops. (Test it if you don't believe me, but if you haven't got a 21-step or other measured density guide,,,,,,, how are you going to test ???? Nowadays folks make a digital step guide... which I'm not fond of because I trust the 21-step with its known density range more, but handled rightly it should be fine, surely better than guessing.)


Presumably you have a mortar & pestle. Skip the pestle, put a measured amount of dry pigment into the mortar than add measured am't of gum arabic, thinned with a measured amount water. (Choose your starting amounts depending on thickness of gum, am't of pigment, desired thickness of emulsion, etc., but don't add enough liquid so anything "floats"!!!) Then you brush briskly with a wretched old round bristle brush, and I do mean bristles. The one I use says Robert Rebetez Basel #270 on it, probably because it's 270 years old. The bristles are stiff & the ratty old thing comes to a point, sort of, but it's ugly and horrible & stiff and perfect for the job... Just scrunch the mix around in that white mortar bowl til it seems smooth to the eye, maybe 3 minutes, depending on volume, then scrunch another minute or so, add about half the volume of saturated ammonium dichromate solution & coat some paper to test.

If you don't have a mortar, put the ingredients together in a cup, stir well, then empty onto a sheet of heavy glass or an enamelled butcher's tray-- that's a flat tray about 8x12 inches with low rim around it -- enough to keep your liquid from spilling over, but not high enough to interfere with smooching the stuff around with a pallette knife until it's amalgamated... maybe 3 minutes, depending on volume.

The amounts above are purely arbitrary depending on your volume of pigment and its fluff, or density, plus the viscosity of your gum, as well of course as your style of printing. The important thing is to measure what you add and then modify amounts accordingly. I note however that this is for gum printing. If you're doing this for carbon printing, I don 't have a clue -- EXCEPT I've probably read or skimmed 90% of the classic carbon formulas. I don't recall any that called for sugar. Who is this sugar advisor? A Cuban?

Oh, and that grinding with a brick stuff is nonsense for any process. (Unless you want bits of brick as pigment, which could have a nice texture.)

BTW, the pigment should be neither sinking to the bottom nor floating on the top, rather an even amalgamation, like, say, chocolate syrup. But come to think of it, what process are you adding dissolved gelatin to? Gelatin at room temperature tends to set ... then what do you do with it? Is this some special gelatin process? In which case, I never heard of it, so ignore everything I've said above.

cheers,

Judy



On Sun, 10 May 2009, phritz-phantom@web.de wrote:
i mostly use dry pigment for all my alternative processes. i started using it, because of a misconception that most alternative photo printers prefer it. later i learned that it just the opposite is the case. but actually i want to keep using it. it's way cheaper (i can buy 80gr of lamp black - which lasts a long time - for the price of on 15ml tube) and i already bought about ten jars. so far i haven't had any problems with printing gum (i put a little bit in a jar, mix it with gum and dichromate with a brush - no problems, no specks at all). but sometimes with carbon i get these specks (i'm not really sure if it's the pigment or the sugar in the mix (i use a rather high sugar content). i filter the carbon solution through a piece of nylon (? - the stuff women's stockings are made of), but still - mostly with the last tissue of the batch; of course the specks go down to the bottom. my normal procedure is to first mix the pigment with a brush and a dash of water, then grind it with a brick and mortar, then put it into the gelatine + sugar solution. i tried grinding the pigment in a little bit of gelatine solution, but using water was better. i once put a little big of alcohol (it's an old bottle labeled "brennspiritus" ("ethanol") i inherited from my grandfather, but i don't really know which kind of alcohol it really is, it's ages old) into the pigment mix and this had the good effect that the pigment sinks to the bottom, instead of swimming on top of the water. it makes the mixing a lot easier. what else could i add that would make the mixing and grinding easier. i haven't added any alcohol or whatever to my pigment mixes for alt. processes so far, because i'm afraid it could interfere with the process.