U of S | Mailing List Archive | alt-photo-process-l | Re: Acids

Re: Acids

As an addendum to your prologue but merely a thought more than fact, when Demachy was using lemons they most likely
were French lemons . . . right? There are many types of lemons though I'd say in those days the variety we can obtain today
is far greater. Lemons do vary in acidity due to time of year, maturity and ground composition. My extremely limited knowledge
says the variance is not great but it is known that the lemon is the most acidic of the citrus fruits, including the grapefruit. The pH
of a lemon is around 2± and I'd wager Demachy knew what lemon would work best.
Just a thought.
Jack F

On Sep 7, 2008, at 7:41 AM, Christina Z. Anderson wrote:

Thanks DJ and Jack,
I guess this is my preamble and question:
Demachy used lemon juice to speed up and make a gum layer more stable for exposure. Thus he employed whatever it is in lemon juice to do so, which was the original request that Loris had--how to make use of a more acidic solution to speed up a gum layer since he is using paper negatives.
In the convo, Marek said that it isn't the acid that is doing the speeding up but Vit C causing a  "chemical fog"--the difference being the first would equate to image exposure but the last would be overall non-image insolubility, not a good thing in my book--but it is because Vit C reduces dichromate says Marek.  I think this is a very fair assessment of my experiment because my criticism was the overall "blahness" of the steps in the step wedges and what I thought was low contrast would be non-image exposure as he says seem right on the money. .
Thus my question is really what acid does not contain a dichromate-reducing agent like Vit C so one could see if acid is a helpful speeding up agent to plop in the mix, and, in fact, if this addition behaves differently than letting gum get acid and stinky--the latter which I would NOT do because I have a very sensitive nose and the smell is SO horrible I just can't be around it. Hey, and I even like Limberger cheese--it is way worse than that.
This is a theoretical subject, of course, because I don't even use full strength ammonium dichromate in my mix--only a 15%, so I personally would use the full strength if I were to use paper negatives. But perhaps Loris is already using a 30% and since I have all 4 acids here it wouldn' t hurt to do a little itty bitty step wedge to divert me from my work at hand....
Christina Z. Anderson
----- Original Message -----
Sent: Sunday, September 07, 2008 3:53 AM
Subject: Re: Acids

I'm not sure what you mean by 'pure' acid... If you mean pure as in 'concentrated',  you end up with solution in e.g. water of acetic acid: In the most concentrated form this is sometimes referred to as 'glacial' acid. Sulfuric acid actually only excists when dissolved in water: SO3 (a gassous product that forms when burning pure sulfur) in water forms H2SO4 (=sulfuric acid). This can be bought in different concentrations. The most 'pure' form then depends on the maximum solvability of SO3 in water (98%). Wen dissolving SO2 in stead of SO3, you get sulfurous acid. 

Also hydrochoric acid (HCl) is, in pure form, a gas. It is formed when common  salt (NaCl), reacts whits sulfuric acid. By dissolving this gas into water, one obtains hydrochloric acid in dilluted aquaous form.

There are pure acids that are available in crystalline (i.e. powder) form. The can be used undissolved in water to use for all kinds of (chemical) processes, but still it usually only can undergo reactions in aquatic contions. The reason for this, is that Acids need to have a liquid environment in wich the acid itself can release a proton : H+, that is the actual acidic component.
The basis rest-molecule can the either be disposed os when your acidified product if produced in the solution as a crystal (filter of the liquid and dry), or as a gas (fumes can then be resolved bu suction and storage in a liquid form onder pressure, or in a solution.

Even water itself has acid properties: H2O becomes H+ and OH-. Since there are no other molecules left in this 'solution', and the basic characteristics of OH- are equal to the acidic characterstics of H+, we've defined water as pH=7. 

So a reference to pure acids, usually means a reference to some kind a solution, without any other substances  mixed in the solution. So no polution with other chemicals. The need for 'pure' acids by means of fully concentrated acids in chemistry is for as far as I know, only needed very sometimes in very specific processes... When pure acid is mentioned, be sure te check what concentration is needed. Dilute stronger acids with pure water (no tap water bu de-ionised or demineralised water, you the kind I mean. 

And mixing the most concentrated form of nitric acid and hydrochloric acid, (VERY!!! carefully) forms aqua regia, king's water. Indeed this acid (it's a mixture of acids, so no pure acid in terms of 'only one substance dissolved in water'), but it's still an acid not polluted with other stuff, so in my opinion, you could still call this a pure acid. Indeed it dissolves and reduces gold and platinum... But if you're trying to make your own gold- or platinum solutions.... This would be accompanied by a very loud: DO NOT TRY THIS AT HOME. Even in the most advanced laboratories, this still is a very complicated and dangerous process....

I hope to have clarified the term 'pure acid' a bit from a chemical point of view. Maybe much to complicated for some of this members, sorry 'bout that!

hope to have answered your question, but let me know if there are additional questions!

kind regards,

Dirk-Jan (or deejay, since my name is so Dutch, other-language based people usually cannot pronounce it, and deejay has even in holland been my nickname since highschool :-))

2008/9/7 Jack Fulton <jefulton1@comcast.net>:
> I'm not Mr. Acid-Expert but  'pure' acid is one unadulterated, or diluted,
>  with water.
> (And, to be honest, I am not sure that all acids are miscible with water but
> I'd say they are)
> Glacial basically means that: without water.
> Formic acid is what ants lay down as a trail and they consist a bit of that.
> Acetic acid (in photography we use a diluted form but can purchase it as
> 'glacial') is similar to that in vinegar which is generally a 5% solution
> Hydrochloric (often times, and in hardware stores called 'muriatic') acid is
> what we have in our stomachs (gastric acid)
> Sulphuric (sometimes in US, 'sulfuric') is used in batteries for autos in a
> dilute form
> Nitric acid is very strong and able to reduce metals
> Then a really strong combo of nitric and hydrochloric (1:3) is called aqua
> regia (king water) and that can reduce gold and platinum but even though it
> is a mixture of acids I don't think it is technically an acid.
> Jack F
> On Sep 6, 2008, at 6:59 PM, Christina Z. Anderson wrote:
> What might be a pure acid?  Glacial?  Or sulfuric or phosphoric? Or
> hydrochloric?  I have all four here...
> So you are saying that sodium ascorbate (isn't that what Vit C is) is
> present to a significant amount in lemons to make more of a difference than
> the actual acid in lemon juice?
> So the test would be lemon juice against other acids?
> Interesting...
> This is what is so useful about this list...
> Chris
> __________________
> Christina Z. Anderson
> http://christinaZanderson.com/
> __________________
> ----- Original Message -----
> From: Marek Matusz
> To: alt-photo-process-l@usask.ca
> Sent: Saturday, September 06, 2008 7:05 PM
> Subject: RE: gum preservatves
> Chris,
> Very informative experiment. I do not think that effect is due to acidity. I
> would rather put out a hypothesis that the effect is due to the vitamin C
> (ascorbic acid) present in lemon juice. Vitamin C is a strong reducing agent
> that would react quickly with dichromate reducing it to Cr (III) and making
> gum insoluble. Kind of like a dark reaction in gum, no light needed. It
> appears as a stain, but it really is not. It is really a chemical fog. 
> ANyways to test acidity one would use solutions of pure acids.
> Marek
>> Date: Sat, 6 Sep 2008 15:49:18 -0600
>> From: zphoto@montana.net
>> Subject: Re: gum preservatves
>> To: alt-photo-process-l@usask.ca
>> Here it is:
>> http://christinazanderson.com/Text_page.cfm?pID=2076
>> Scroll down to the very bottom past the color charts.
>> I'm not saying it proves anything, but acidity may account for some
>> problems 
>> that people say are issues with gum, and it is only really meaningful in 
>> relation to the water control strips done at the same time with the same 
>> amounts of dilution. Otherwise a lot more tests would have to be done to
>> be 
>> conclusive. If, as Ryuji and Demachy said, there is a reduction to
>> chromic 
>> acid with the addition of lemon juice, which I don't know because I am not
>> a 
>> chemist, I don't know if that is speedier or less speedy than dichromate.
>> Chris
>> __________________
>> Christin a Z. Anderson
>> http://christinaZanderson.com/
>> __________________
>> ----- Original Message ----- 
>> From: "Loris Medici" <mail@loris.medici.name>
>> To: <alt-photo-process-l@usask.ca>
>> Sent: Saturday, September 06, 2008 3:13 PM
>> Subject: Re: gum preservatves
>> Thank you!
>> Now that you say that, I remember the section about it in the "Learn" part
>> of your former website. (Adding lemon juice and staining... I'm not making
>> it up right?)
>> Judy's note on sizes was interesting and real food for thought, BTW.
>> Ryuji's notes also were interesting -> I mean the probability of citric
>> acid (or any other organic acids) interacting with dichromate in an
>> unwanted manner. That powered my original position which was increasing
>> the acidity by not adding alien compounds... (Still don't know if that can
>> work or not -& gt; I may do some tests in the future if the exposure times
>> become unbearable to me and/or I can't do nice casein prints...)
>> Regards,
>> Loris.
>> 5 Eylül 2008, Cuma, 1:12 am tarihinde, zphoto@montana.net yazmış:
>> >
>> > ...
>> >
>> > Have at it, Loris. I found that the more lemon juice drops
>> > I added to the mix (with drops of water added to the control
>> > group in the same proportion) that I got lots of staining of
>> > the highlights and lower contrast, but with paper negs this
>> > might be helpful to you--I mean, the lower contrast part.
>> > Step wedge steps were not too differentiated.
>> > Chris
>> >
>> > ----- Original Message Follows -----
>> > From: Loris Medici <mail@loris.medici.name>
>> > To: alt-photo-process-l@usask.ca
>> > Subject: Re: gum preservatves
>> > Date: Thu, 04 Sep 2008 21:37:54 +0300 (EEST)
>> >
>> >>David & Chris, that also arrived to my mind just after had
>> >>sent my last message... Even if I refrain to introduce
>> >>another alien compound into consideration - as a first
>> >>impression -, it sounds interesting / promising. You can
>> >>bet I will try this (with citric acid)as soon as possible!
>> >>Of course there's also the staining issue... I'll see.
>> >>Thanks!
>> >>
>> >>Chris, do you know how much lemon juice was Demachy adding
>> >>to his gum?
>> >>
>> >>Regards,
>> >>Loris.
> ________________________________
> Get more out of the Web. Learn 10 hidden secrets of Windows Live. Learn Now