LASREVER REVERSAL bleach

Dichromate bleach--is sulphuric acid the only acid that will work or will any sufficiently strong acid with with sodium dichromate in particular or in general potassium or ammonium dichromate.

If so, why? or if no, why and what else is worth trying, particulary acetic acid, since it's readily available.

I've been able to use reversal bleach which is quite diluted from the recommended concentrations (this is the sulphuric acid stuff).

My question is--can ANY sufficiently strong acid work? Are they any that should be avoided due to chemical reactions?

Any people tried this and had any results good or bad or catastrophic?

c'mon...I can't believe NOBODY knows..where's our chemistry xperts?

I'm run almost out of the "good stuff" and now i need to either get sulphuric from the battery place or find an over-the counter substitute...WANT the substitute if possible...don't want to mix and end up with guys with devo suits taking me out of my apartment and being charged with who knows what....

please...somebody must know SOMETHING about this1!!!!

johnielvis said:

Dichromate bleach--is sulphuric acid the only acid that will work or will any sufficiently strong acid with with sodium dichromate in particular or in general potassium or ammonium dichromate.

If so, why? or if no, why and what else is worth trying, particulary acetic acid, since it's readily available.

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One of the criteria to look for is that the acid must not be oxidized by the dichromate.
Toluene sulfonic acid would be something to try. It did work nicely to (reversal) bleach holographic/Lippmann emulsions (but I don't see why it wouldn't work with "normal" photographic emulsions.

As for acetic acid it's not strong enough an acid to form a reversal bleach with dichromate. However, potassium CHROMATE + acetic acid + potassium bromide forms a very stable rehalogenating bleach. See: http://holoforum.org/oldforum/viewtopic.php?f=2&t=6336

that's what I've HEARD, but I've been able to dilute the sulfuric quite a bit from recommended dosages, so that's what kind of led me to believe that maybe acetic may work.....

how about this...i try to do it with acetic is there any nasty smells or black smoke or poison gas that can be generated maybe?...I'll likely do this OUTSIDE if nobody sees a nasty objection...I'm thinking it just MAY work....

acetic is avaiable...battery acid is more available than that solfonic stuff---don't even know where to get that from


hydrochloric plus dichromate gives you INTENSIFIER.....so that's the weirdness that's got me with the questions...how come one acid makes it a bleach and one makes it an anti-bleach? how do you tell what does what? except from experimenting???

You can substitute sodium hydrogen sulfate (sodium bisulfate) for the sulfuric acid. You can get this cheaply since it is used to lower the pH of swimming pool water. As pointed out you cannot use any organic acids like acetic acid since they will be oxidized by the dichromate. As far as inorganic acids your choice is really restricted. Rule out nitric or hydrochloric acids.

Gerald C Koch said:

You can substitute sodium hydrogen sulfate (sodium bisulfate) for the sulfuric acid. You can get this cheaply since it is used to lower the pH of swimming pool water. As pointed out you cannot use any organic acids like acetic acid since they will be oxidized by the dichromate. As far as inorganic acids your choice is really restricted. Rule out nitric or hydrochloric acids.

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NICE...that I have---do you know offhand where some recipes for quantities/concnetrations are? that will work out great--I got some of that laying around right now and I can try it tonite!!!!!

THANKS---anybody got the bisulfite recipe so I get results first time?????THANKS!!!

oh---bisulFATE....that I gotta check...blast...another one I gotta track down...I think maybe I've seen that at helix..so it' s not out of the question....OH..right swimming pool lower the ph...THAT's where I can score some---theres a swimming pool place that I get hypo from I can try...

OKK--still need the recipe..how many spoons of sugar will make the medicine go down?

You can think of 1 mole of sodium hydrogen sulfate NaHSO4 as containing 1/2 mole of sulfuric acid, NaHSO4 = 1/2 Na2SO4 + 1/2 H2SO4. Therefore 120 g of sodium hydrogen sulfate are the equivalent of 49 g of concentrated sulfuric acid (49 g/1.84 g/ml = 26.6 ml). For the monohydrate use 136 g.

This appears to use potassium-permanagante, but perhaps it's a starting point.

http://www.photosensitive.ca/wp/bw-reversal-processing-notes

There are a lot of really dense threads about this topic, and I'd bet you could dig something out if you search hard enough.

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So far I haven't seen it in use with dichromate.

and hey, I just got it.. LASREVER!

ok...looks like sodium hydrogen sulfate dissolves to 1/2 neutralized sulphuric acid....which sounds like it should work as long as the sodium floating around in there don't do anything bad.

looks like a trip to the pool supply store is in order.

so, since it's 1/2 neutralized--I take this as being concentrated sulphuric acid at 1/2 strength then? or how would that work out for dosing this stuff as a substitute?

How much sulfuric acid and at what strength does your formula require?

The key to B&W reversal processing is to remove the negative Silver metal image completely after the first developer. One of the methods used is to oxidize the Silver metal to form a soluble Silver salt. The best salt to form, one which dissolves in water is Silver Sulfate and thus you have the need for Sulfuric Acid.

So, the best bleach is Sulfuric Acid + some oxidant. The best oxidant is Dichromate ion and the second best is Permanganate. There are other acids and oxidants, but you must never use one containing Ammonia in any form or you will dissolve part of the positive image and lose detail.

PE

johnielvis said:

ok...looks like sodium hydrogen sulfate dissolves to 1/2 neutralized sulphuric acid.

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Actually this is an oversimplification to aid in the calculation.

johnielvis said:

which sounds like it should work as long as the sodium floating around in there don't do anything bad.

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What is needed for the bleach are hydrogen ions which the sodium hydrogen sulfate readily supplies.

NaHSO4 --> Na+ + HSO4-
HSO4- --> H+ + SO4-

The sodium ions aren't going to hurt anything.

OF course...!!!!!

I"m using sodium dichromate---OBVIOUSLY sodium ions won't bother....bluh...
anyways...the formula that I want to use as a starting point is the one in anchall's 3rd book:

potassium dichromate, anhydrous, 6.0g
water to make = 1.0 litres
sulphuric acid, concentrate 12.0 ml

now I'm substituting sodium dichromate for the K...

given that, how much of sodium hydrogen sulfate do I need to make this strength of "acid"?

johnielvis said:

I'm run almost out of the "good stuff" and now i need to either get sulphuric from the battery place or find an over-the counter substitute...WANT the substitute if possible...

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I don't know man; battery acid is dirt cheap here. Why substitute? Do you have some expensive Hazmat surcharge to pay?

Concentrated Sulfuric Acid is about 99%, while battery acid is about 35 - 37%. Concentrated Sulfuric acid is hard to get, expensive and dangerous (to non-chemists) while battery acid is easy to get. So, get battery acid and use 3x more removing 2/3 the amount of water from the formula.

So, in the Anchell formula which calls for 12 ml of "concentrated" acid, you would use 36 ml of battery acid and you would reduce the added water by 24 ml. Not much of an error really when you consider the "slop" in this particular formula.

PE

I mean how much of the sodium hydrogen sulfate would I need to get the above concentration of 12ml conc per 1 litre solutuion....

oh--that 99%...that means 99% by weight is h2so4? I had no idea that it is like a pure acid liquid wiht no water....interesting....I already know how to dilute a diluted liquid...yes...

however I do not want to hunt for battery acid--I want to use the dry acid if it works...now..thats NaHso4....how much of THAT do I need to get that 12ml equivalent hydrogen?

I'm thinking get the weight of 12ml of concentrated and double it...that should be close....let me know if I'm WAY off here, but that seems reasonable

12 ml x 1.84 g/ml = 22 g. 22 g / 49 g x 120 g = 53 g of anhydrous sodium hydrogen sulfate or 61 g of the monohydrate.

I have suggested using this dry chemical because their are places where even the shipping of battery acid is a problem. The dry chemical is also safer for most people to use.

magnifique--thanks Jerry--you are of the same opinion as I currently am and same battery acid finding troubles...I just want no hassles now or in the future (which hassles always increase)

now what's with the 120 grams thing up there? I don't understand what 120 grams is...let me think about it anc calculate the molecular weights and see what numbers mean what there.....my thinking above was that, ball park, if we have 22g of h2so4 and it's like equivalent acid strength of the dry acid is 49g (above number, almost double the 22g) then I want 49 grams of it mixed in there, right?...let me do some cipering as jethro says...

my logic would be 22g * 2(roughly) = 44 grams for approximate same acid strength,



now..at the pool supply place--how do I tell the anhydrous from monohydrate? is it like the hydrated stuff has like bigger chunkier crystal shape? I'll go looking for pics...or--what is sold as "dry acid"...I'm assuming it's the monohydrate for home use---more stuff=less strong..less hazard...less chance of dust/sniffing the stuff.

how to tell the difference?

The MW of sodium hydrogen sulfate is 120. The concept of a mole is pivotal to any calculations about chemical weights. A mole is the molecular weight of a chemical expressed in grams. Therefore 1 mole weights (Na = 23, H = 1, S = 32, 4 o = 4 X 16) 120 g and for the monohydrate 138 g. From the balanced equation you can see that 1 mole of the salt forms 1/2 mole of sulfuric acid. The MW of sulfuric acid is 98, so half that expressed in moles is 49 g/mole. Since your formula calls for a liquid volume of conc sulfuric acid we must adjst for its density 1.84 g/ml. If you carry the units thru your calculations and cancel them out when appropriate you can see whether the calculations are correct or not. For example, in the final calculation to determine the amount of liquid you have (grams) / (grams per milliliter). The grams calcel out of the equation being in both the numerator and denominator leaving only ml which are the correct units.

It should state on the label whether it is the monohydrate of the anhydrous form.

Dod't just toss numbers around, you first need a balanced equation and the MW of all the important chemicals. You may need additional information such as the liquid density in this case. The math is straight forward once you understand what needs to be done.

THANKS...I would have made me WORK for the answer--just got to work where I got my periodic table/chem books.....yes..it all comes back very quickly...

OH--yes I do agree that correct calculation are absoultely necessary---but I also like to check if I'm in the ballpark by doing what an old instructor of mine called "russian arithmetic"....everything crudely rounded and approximated...

i know when I just got out of school, sometimes you get so caught up in the caluclation, you don't see if the answer is reasonable or not...that takes experience....

THANKS AGAIN...going to the pool place today I hope.