Re: clearing dichromate stain

[Katharine Thayer <kthayer@pacifier.com>]

(No, my mail program isn't suddenly replying to old messages on its  
own, this is something I've been thinking about for a while.  At any  
rate,  it seems like it's about time there was some discussion of  
actual alt-photo topics here).


On Dec 11, 2006, at 6:55 PM, Christina Z. Anderson wrote:

> Heheheh, Charles,
>
> Here's my complete notes on clear ingredients from 1898 to present  
> day times.  Have at it. BUT for what it is worth, I don't clear.   
> And, if I were to, I use the potassium metabisulfite, finding it  
> infinitely better.
I'm puzzled; infinitely better than what?  Since it's been  
established  that there's no functional difference between bisulfites  
and metabisulfites --metabisulfites become bisulfites once in  
solution-- I'm not sure on what basis potassium metabisulfite could  
be said to be "infinitely better"  than a bisulfite.    I once took  
at face value Livick's assertion that potassium metabisulfite is  
better than sodium bisulfite, but when I did comparison tests of my  
own, I found no difference in effectiveness of clearing, speed of  
clearing, softening of the film, or noxious odor,  between sodium  
bisulfite and potassium metabisulfite, and since we've been told that  
there's little if any functional difference between them,  it makes  
sense that I observed no practical difference between them.   
(Chemists will correct me, I trust,  if I'm wrong about that).  I  
once opined here that potassium metabisulfite didn't smell as bad as  
sodium bisulfite, but I was brushing it on at that time rather than  
bathing it, and when I compared the two in  trays, they smelled the  
same, and equally strong.

As for alum, does anyone even use it?   I had never tried alum for  
clearing, never saw any reason for it when bisulfites work well, and  
as far as I can tell from the compilation below, its use has been  
discouraged for at least the last 50 years or so by most writers.   
Whether the reason they give, compromised archivality of the paper,  
is justified, I'm not sure, but my own comparison of last evening  
shows a clear superiority of bisulfite over alum for clearing. (I'm  
assuming that the "alum" that's meant when no specific alum is named,  
is the "common alum" containing potassium and aluminum; that's what I  
used. I don't have any chrome alum on hand at the moment to see if  
that works any better.)  It seems to me that alum, at least this  
common alum,  works differently from the bisulfites, in that it fades  
the stain to lighter tan over time (just as does plain water) rather  
than clearing the stain to pale blue-grey, as do bisulfites (and  
sulfites, given enough time).   I'll post this comparison soon.

 Different assertions have been made about what is actually going on  
when we're clearing dichromate stain.  Someone in a recent thread  
said that we're reducing dichromate stain to Cr(III); Sil Horowitz  
seems to be asserting (in a somewhat garbled secondhand citation  
below)  that it's already fully reduced and is inert.  A physical  
chemist I  talked to about issues around the chemistry of the gum  
process speculated that it might consist of transition products, in  
other words partially reduced but not completely reduced chromium  
species. An analytical chemist once told me that probably what we're  
doing when clearing with bisulfite is to convert whatever insoluble  
chromium entity constitutes dichromate stain into  chromium sulfate,  
which is more soluble and can be washed away.   This makes some sense  
to me, since I've observed (and Sarah Van Keuren, below, seems to  
have also observed) that  the product of the reaction, when there's  
enough stain to  see the product,  is blue, and we know that chromium  
sulfates are blue. But as the chemist said,   it's kind of hard to  
know what the reaction is when we don't know what one of the  
reactants is  (as far as I know, no one knows exactly what dichromate  
stain is, chemically, and the diversity of opinion about this  seems  
to support  my suspicion that we don't have a clear idea of what it is).

Katharine




> "IF creamy yellowness of chromate stain is not desired, use alum,  
> sulphite of soda, or hyposulphite of soda, strenght being  
> immaterial with a careful after washing. If the print is only just  
> sufficient or only slightly overprinted, care must be taken that  
> the clearing bath is not acid, neither must the washing be too  
> prolonged, but if the print is first dried and submitted to light,  
> this precaution is unnecessary." (Barnet, p. 252)
>
> Clearing:  1-2 mn in 5% sod bisulfite.  Alum is also used but  
> clears slowly. He recommends drying first after clearing and before  
> the final wash to stabilize the prints, and then wash for 10 min.   
> (Wenzel 91)
>
> 2% alum for 10 mn.  He says alum has a tendency to crystallize and  
> emphasize each grain of paint in the image, and so coarsen it.   
> 72-73.  Bisulfite of soda 5% will work.  So can hyposulfite be  
> used, but it must be thoroughly eliminated by a prolonged washing  
> (Warren 73)
>
> It is necessary to rid the paper of chromic salts for its future  
> permanence (Maskell 39)
>
> Immerse dry print for one or two minutes in water to which has been  
> added sufficient bisulfite of soda to produce a distinctly  
> sulfurous smell.  Wash a minute or two after because bisulfite of  
> soda is extremely soluble. (Maskell 39)
>
> 1-25% alum but 5% seems about right; 5-10min. If film is soft, dry  
> first and alum thereafter, otherwise alum right away.  Clear:  5%  
> bisulphate of soda, 2% alum, 5% hypo.these harden pigment and  
> remove dichromate.37 Abbott
>
> Alum bath:  1:20.  Or mix equal parts of A and B:  A soda sulphite,  
> 1 oz in water 3.5 oz, and B sulfuric acid 45 minims in water 3.5 oz.
>
> 1% bisulfite of soda for a few minutes. 189 Demachy, Modern Way.
>
> Alum bath is not necessary because the stain disappears of its own  
> accord when the print has some time been exposed to light. P. 62  
> Richards.
>
> Clear:  alum 1:20 or sod bisulfite 4%. P. 70 Richards
>
> He says alum destroys some of the finer particles of pigment and  
> leaves a coarser grain behind, so recommends sodium bisulfite 5%.  
> 114 Richards
>
> Clear:  5% alum, or 10% sod sulfite.Lambert + Cummings
>
> 5% potash alum or sodium bisulphate clear, and after rinse; best  
> left until the final printing is complete as it cause slight  
> contraction of the paper. 240 Bayley
>
> 1 oz alum to 20 oz water for clear, or small amount of sod  
> bisulfite-2-3 tsp in a tray of 60 oz.  Alum bath tends to shrink  
> the paper so don't use it til end.  Libby P. 129.
>
> When print is done developing, immerse in concentrated white alum  
> to remove yellow and then rinse off and lay out in the sun to dry,  
> which will fix the emulsion from further development. Matson P. 44.
>
> 5% alum clear for 10 min and then rinse Wall 124 1928
>
> He recommends a 10% solution of sod bi or pot metabi, done after  
> the finished print has been dried.  He does not like a 10% alum  
> because the hardening effect does not appear until the film is dry  
> and the film is hard enough when it dries anyway,  nor does it  
> remove the stain very easily. Anderson Sept 1935 P. 145.
>
> Pot metabi 5%  more effective than alum or sod bisulfite. Henney  
> 1939 P. 492.
>
> Alum clear:  1 oz to 16 oz.  Hardens surface and clears out stain.   
> Kilmer P. 148
>
> 5% pot metabi or sod bi; alum should not be used because it  
> threatens print permanence. Clear after print has dried.  Once dry  
> the coating sinks into the surface of the paper and is very tough  
> 207 Crawford
>
> 1 to 16 alum for 10 min, rinse briefly, dry.  Kilmer 153.
>
> He uses a 5% acid hardener, which contains sodium or potassium  
> bisulphate and chrome alum, which clears the stain and hardens the  
> gum.  49 Frederick
>
> Pot alum clear 25g to 1000, or 15g alum pot sulfate to 300 ml, or  
> 5% pot metabi or sod bi, because an alum bath does not promote  
> print permanency. 75 House
>
> Soak print in 2.5% pot alum or pot chrome alum for 5 mn to remove  
> stain. Pp. 58-59Gassan Lt Imp.
>
> 1% sod bi clear. P. 192.McDonald
>
> 5% pot metabi for sev minutes and 30min wash.  Alum also, but not  
> archival. Arnow 127.
>
> Clear with 5% pot metabi, not alum because alum is harmful to the  
> paper surface and to the permanence of the image.  71 Reeve
>
> Sod bisulfite 2-5%, sod metabi is less odorous, pot bisulfite also  
> 25Nadeau
>
> Chrome alum , called chromium potassium sulfate, dark violet, 5% in  
> water hardens gelatin.  Does not keep in solution and should  
> therefore be replaced twice a day and never stored as a solution.   
> 25.  Nadeau
>
> If print is intended to be permanet, stain should be removed.   
> Thick rag papers hold the di more, esp if dev was short and cold.   
> 40Nadeau
>
> Greenish stain could PROBABLY  be removed by .5 to 1% hydrochloric  
> or sulfuric acid, but it is chromium oxide and is  a permanent  
> pigment and should be of no concern.. 40.Nadeau
>
> Dichromate left in print needs to be removed because it damages the  
> image. Sod metabi and sod bi both can be used but require longer  
> wash times than pot metabi because of their lower solubility.  Pot  
> alum used, too, but requires increased washing than all others, and  
> also seems to alter the image color, losing some if its soft  
> delicate effect.  It threatens print permanence (he sources Wm  
> Crawford). 42 Scopick
>
> How long a print can remain stable without being cleared is not  
> established. You can confidently store prints for one year without  
> visible change.  64 Scopick
>
> Reuse clearing bath until it turns muddy green and then discard.   
> 66 Scopick
>
> 1% sod bi or pot metabi clear. P. 45. Davis II
>
> 5% pot metabi and 5 mn wash 163Farber
>
> 1% pot metabi; 5% is too strong.  20 min wash after Livick online
>
> 5% sod bisulfite, a weak acid, sets and cures the image.  Heavy  
> dark tanning does not clear entirely but turns a pale blue/green.   
> She uses 2/3 c sod bisulfite in a gallon.  You can partially clear  
> the tans if you want some duotone effect.  Heavy dark tanning does  
> not clear entirely but turns pale blue/green.  Use the sod bi (2/3  
> c to a gallon) until it turns blue green and then discard.  P. 5  
> Van Keuren
>
> Fix print with short exp to UV after final dev.  Any remaining di  
> will fix gum left behind.  Don't do too long or you'll fog it (?)  
> 170 Barnier
>
> 5% pot alum bath to clear, or 10% pot metabi or sod bi for 5 min..  
> 120-1 Blacklow
>
> Pot metabi 1%; sod metabi and sod bisulfite are ok but they soften  
> the gum emulsion.7Mix pot metabi with distilled water Livick 50
>
> You can spray on a clear of pot metabi, or selectively paint it on  
> in problem areas.  Pot alum is not archival.  238 James
>
> 5% pot metabi for 2-5 min, 15 mn wash 176 Hirsch
>
> 5% pot alum, altho it may degrade image. PF 1, 17
>
> Sil Horowitz says that the dichromate is already fully oxidized and  
> is relatively inert.  PF 6 36"
>
> ----- Original Message ----- From: "ryberg" <cryberg@comcast.net>
> To: <alt-photo-process-l@usask.ca>
> Sent: Monday, December 11, 2006 12:54 PM
> Subject: clearing dichromate stain
>
>
>
> > Folks,
> >    The usual recommendation for clearing dichromate stain is a 3%  
> > or so solution of sodium bisulfate.  In her "Condensed Alt  
> > Processes" book Christina says "some use 5% sodium sulfite" but  
> > that didn't work for me. Do I remember correctly that sodium  
> > sulfite plus sulfuric acid makes sodium bisulfate?  (My last chem  
> > class was 50 years ago.)
> >    Also, I have a very dim recollection that a weak hydrochloric  
> > acid bath is supposed to work--or have my gray cells misfired?
> >    Bisulfite is a mail order whereas sodium sulfite and  
> > hydrochloric acid are available within a couple of blocks.
> >    There is no sunshine and won't be for many months here in  
> > Portland OR.
> > Thanks for any help.
> > Charles