hypochlorite and other bleach agents (was Eau de Javelle)
First of all, the strength of household bleach varies depending on the age and storage condition. It's usually about 5% but there is no point to be exact about this. Also, depending on the manufacturer of the hypochlorite and the manufacturing method, the inert ingredients vary a lot as well. Most common byproducts and additives are sodium chloride and one or more of alkaline agents. From: etienne garbaux <photographeur@nerdshack.com> Subject: Re: Eau de Javelle ( Javel ) Date: Mon, 26 Nov 2007 16:32:37 -0500 > Hypochlorite in solution is kept at least slightly alkaline > to prevent the release of chlorine gas. Household bleach is > generally made alkaline by hydroxide (a byproduct of the > industrial process by which the hypochlorite is produced) > rather than carbonate. Assuming that the alkalinity is the > reason for the carbonate in Javel water, household bleach at > the appropriate dilution should be a fine substitute as it > is. You may want to play with the dilution, depending on > the process. If you wanted to reduce the alkalinity, you > could add small amounts of hydrochloric acid while > monitoring the pH (you would NOT want to go so far as to > make the solution acidic). The reason to make bleach solution alkaline are multi-fold and not just because of chlorine outgassing. At lower pH, hypochlorite becomes hypochloric acid, which has considerably lower standard reduction potential (-1.5V vs -0.95V) and hypochloric acid is a more aggressive oxidizing agent. The acid form is also more reactive with cellulose fiber than the anion form. However, this is only relative and both forms can attack fabric. It's just that the acid form does so faster. > Photographic hypo (sodium thiosulfate) decomposes > hypochlorite and could serve as a wash aid. (If you were > not using the hypo as a silver fixer -- i.e., to dissolve > remaining silver halides -- you would not form the complexes > that are so hard to wash out after a thiosulfate fixing > bath.) Use of hypochlorite or any oxidizing agent as a "hypo eliminator" is strongly discouraged from archival viewpoint. It's better to leave prints poorly washed than treating them in oxidizing agents. (This paragraph for silver gelatin process.) You don't want to use thiosulfate in order to terminate bleaching action, either. From: Dan Haygood <dan@haygoods.org> Subject: RE: Eau de Javelle ( Javel ) Date: Mon, 26 Nov 2007 08:04:01 -0700 > I once had occasion so soak some whites (laundry) in > household bleach & water for hours. The clothing, cotton > and cotton/poly, came out of the following wash with some > tears in the fabric. The clothing proceeded to disintegrate > in subsequent washings. This is a well known shortcomming of chlorine-based bleach. If you come up with a way to overcome this without impairing the bleaching/disinfecting power, you'll become rich. Generally, hypochlorite bleach should be diluted with cold water and used in cold solution. Only time I use hypochlorite bleach hot is when I want to maximize the disinfecting power in cleaning my kitchen surface, sponges and such. I also use hot hypochlorite bleach to disinfect the laundry washer. The invisible side of those perforated drums and other invisible surfaces in the laundry machines are biologically dirty and I don't want them to adsorb on my clothes. > I could not find much info on the internet for the phenomena > of bleach-rot, but this article discusses it and mentions > two "stop-action" chemicals to clear bleach (Bleach-Stop and > Anti-Chlor). > http://labricoleuse.livejournal.com/11816.html The above website states: | Bleach manufacturers don't like to acknowledge the fact | that bleach can damage the integrity of some natural | fibers, but it's true. I'm not sure whether the author spoke to the right person at bleach manufacturers. Bleach manufacturers are flat out researching more efficient bleaching formulation that also minimizes fabric damage. Hypochlorite bleach is also not the most desirable agent to use in terms of human safety and environmental impact, although it is not as serious as some other compounds I brought up in the past. One alternative compound that is commonly used is peroxide and other peroxo compounds such as percarbonate. These agents work as a mild bleach in very hot water, but the standard laundry water temperature in the U.S. is too low to be highly effective without a bleach accelerating agent. As you imagine, bleach manufacturers are developing efficient catalysts that accelerate bleaching action. Many compounds proposed so far use chelated iron molecules to enhance iron's redox catalysis property and you better stop wondering why I am interested in the bleach chemistry; it is exactly the opposite to photographic developer formulation. However, I think these bleach catalysts proposed so far are too expensive to synthesize (as far as I can think of) and only some of them are in current use. Also, even if the bleach catalysts are used, the bleach system will damage the fabric just like in hot percarbonate solution or hypochlorite solutions. This is primarily due to hydroxyl radical. Hydroxyl radical may be important in the disinfectant action, but not in bleaching, and therefore bleach manufacturers are comtemplating adding lots of cheap hydroxyl radical scavengers to the bleach formulation. Here, their challenge is to find a suitable agent that is cheap, effective in scavenging hydroxyl radical, not irritating to human skin, safe to the environment, and do not react with superoxide (which is necessary in bleaching action). Any reasonable chemist can name compounds that meet 3 or 4 of above but not all 5 of them. In case bleach is mixed in a washer detergent, there can be more possibilities for formulation, because properly formulated laundry detergents always contain molecules that cover up cellulose fibers (antiredepositioning agent). I personally would not use chlorine based bleach in darkroom processing, period. It was once commonly suggested to wash print drying screen and ferrotyping cloth with dilute bleach to eliminate residual thiosulfate. However, in light of modern research in image permanence, this level of effort is nothing but unnecessary (just use water to wash it and that's perfectly fine!). -- Ryuji Suzuki http://silvergrain.org
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