Re: ferri sesquichlorati
Hi, Chris Sorry if this gets a bit long... Ignore according to need :-) I do not have all the info here right now, but intend to make a very brief summary of this process in a couple of weeks... If I get time ... But; first I did probably only do a few attempts with gum, with no result, that was mixing ferric chloride and tartaric acid in a ratio to make ferric tartrate, as I can remember it right now, (that also means I did not follow the recipe properly) this is about one year ago. With gelatine that gave the result in the link I sent. With gum nothing. It is very possible that different concentrations than what I used would have given better results for gum (and for the gel :-). I did several attempts with gelatine, got good edge sharpness but the surfaces where quite uneven, sort of woolly. Possibly thinner layers would work better, but contrast might be high, believe this process, as the pellet process, was used for line drawings and copies. This might be possible to adjust with pigment concentrations or otherwise ... If you have Mike Wares Cyanotype book, have a look on the pellet process. It contains gum, ferric and tartaric acid. It is mentioned somewhere in there that Prussian blue can harden colloids, but have again not found any closer explanations. For gelatine normal cyanotype "hardens" gelatine in thinner layers, but I had less success with thicker layers. (A cyanotype mix in gelatine makes a very thin relief on glass for example, but seems like the gel need to hang onto something in addition, not too strong hardening). How does a normal cyanotype solution mixed in gum arabic work btw ? I have not tried this.. In my experience it is particularly the tartaric acid that makes this works in a "positive manner" - the exposed areas becoming soluble, as mentioned something like this happened when mixing in tartaric acid + AFC in gelatine. It does not happen if mixing in citric acid or "long list of other acids" + AFC in gel, have not tried that with other ferric salts. ______________ some guesses on this.. (and I am not really a chemist so please suggest things anyone..) Fe3+ could, maybe, crosslink, same as cr3+ ... On exposure link breaks, problem is that then the ferrous could be a stronger cross-linker than the ferric. Which is when the tartaric acid could come inn and link up with the ferrous in competition with the gel - maybe. Easy to check, does FeCl harden gel ? Or the tartaric acid alone crosslink's the gel, on exposure it is oxidised by the ferric going to ferrous and the link breaks ... Easy to check, does tartaric acid harden gel ? :-) It is possible that ferric tartrate crosslink's the gel and hardens it, (sort of; gel-tartaric-Fe-tartaric-gel) on exposure the link breaks and the gel becomes water-soluble... Ratios given in the recipe I looked at did not match making ferric tartrate out of the all the ferric chloride, but the recipe I looked at was old and so on... Should be possible to try some tests.. Have not had time to play with this, maybe next life, or in some weeks, but are, obviously, interested.. ______________ The last chapter in "The American Carbon Manual" : HISTORICAL NOTES ON CARBON PRINTING. Have several descriptions of this method, for example: (If you don't have it, there is a word file somewhere.. Or I can mail it..) "The first results of this process were shown to the French Photographic Society, in July, 1860, the process having been patented the month previously. The details were published in the following November.* In this process a mixture of perchloride of iron and tar-taric acid, ten parts of the former to four of the latter, dissolved in one hundred parts of water, is the sensitive preparation. It is poured on a plate of glass which has been previously coated with collodion or other suitable material; it is then left to dry in the dark, and becomes spontaneously insoluble. Submitted to the action of light, however, it again becomes hygroscopic." Goes on to describe what is a "dusting on process".. ________ Seems like I just wrote most of the basis for that "summary" :-) On 10/18/06 9:43 PM, "Christina Z. Anderson" <zphoto@montana.net> wrote: > You all are great! > > OK, so here is what it says: > > Photo American, 1903, A Gum Bichromate Modification: > Dr. Lux has written about this in the Deutsche Photographen Zeitung. > Paper coated with a 12% hard gelatin containing "some acetic acid and some > iron solution", the liquor ferri sesquichlorati (as you say, below) of > pharmaceutical lore. It is added until the color of the mixture is such > that a layer 2 mm thick makes white paper look distinctly yellow. Pigment > then added as usual. Coating done thick and even at 112 degrees F. Expose > and develop as soon as dry. Develop in dark in water til soluble iron salts > are removed, and then do rest of gum print in light. > > Now, of course, he says "gum or other colloid" and proceeds to talk about > gelatin... > > That's about it, and not very clear for sure! > > I have also somwhere a person's process who uses silver nitrate in the gum. > > But Halvor, it sounds like the same in Silver Sunbeam, which I have, so I'll > check it out, and you say no luck with it...interesting. But I did think, > one day, when accidentally using my cyano brush to brush a gum layer on, > what would happen when it was mixed into the layer? > > No mention of dichromate in this mix, though? Weird. Does the ferric > chloride harden the gelatin? > Chris >
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