Muriatic acid question

Discussion in 'B&W: Film, Paper, Chemistry' started by Terrence Brennan, Aug 27, 2012.

  1. Terrence Brennan

    Terrence Brennan Member

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    I bought a jug of muriatic acid for use in my workshop. I found out that it is a slightly diluted form of hydrochloric acid, marked Baumé 20°, and (I think) 31.45%.

    The question is: can this acid be substituted in any way, shape or form in any of the formulas which require sulfuric acid?
     
  2. Gerald C Koch

    Gerald C Koch Member

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    Whether there can be any substitution would be based on knowing the particular formulas. Concentrated hydrochloric acid is nasty stuff. It can cause immediate and serious burns if there is skin contact. The fumes are also dangerous.
     
  3. RalphLambrecht

    RalphLambrecht Subscriber

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    isn't sulfuric acid one of the esiest to get?every hardware store, selling car batteries has it, right?
     
  4. Vaughn

    Vaughn Subscriber

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    Tossing sulfur into the mix when it is not suppose to be there seems a little chancy to me.
     
  5. Worker 11811

    Worker 11811 Member

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    Regardless of whether you find a photographic use for it keep your stock bottle out of the darkroom.

    No matter how tightly you think you have stoppered the bottle, it will emit fumes which will build up in the air and eventually destroy anything in your darkroom that comes into contact with it. Best store it in the garage or some place ventilated. Put the lid on tight then put it in a plastic bag and tie a knot.

    As for an application for it, I have used it as an etchant to make gobos (pattern stencils) for spotlights used on the stage.
    Sheets of roofing flashing are cut into pieces 3 or 4 inches square. They are sprayed with two coats of Krylon spray paint and dried thoroughly, at least an entire day. Best for a couple of days.
    The pattern you want for your gobo is traced onto the painted metal then, using an Exacto knife or similar tool, scrape away the paint where you want the negative space (holes) to be.
    Drop the pattern into a tray of diluted muriatic acid (half-and-half with clean water) until the exposed metal is eaten away. Observe closely and be on the lookout for the acid creeping under the paint lest you get ragged edges on the finished product.
    Remove from the acid, using tongs (chopsticks) and rubber gloves. Neutralize the acid with a solution of baking soda and water then rinse clean with running water.
    Use paint thinner or stripper to remove the paint. Rinse away all traces of chemicals or paint or else, when it goes into the hot spotlight, it will burn. (Ask me how I know this! :wink: )
    Use a jeweler's file or an Exacto knife to clean up any ragged edges or sharpen the corners then you are ready to go!

    Sometimes, when the students at my school are putting on a reprise of a famous play, they like to use that show's logo as a curtain warmer. Using this method, anything you can print on paper and transfer to the stencil can be made into a gobo. Other times, we need a dozen of a certain gobo (like a full-stage foliage breakup pattern) but we only have a budget for one or two. Etching copies out of roofing tin is a good way to cut costs.

    I don't know what use muriatic acid would have as an ingredient in developing chemistry but I don't see why it can't be used as an adjunct or alternative method to producing other photograpically oriented things. (e.g. Etching plates or something like that.)
     
  6. Vaughn

    Vaughn Subscriber

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    HCL (in water) -- used as clearing agent in platinum printing -- and to bleach black spots off of the same.

    I have been platinum printing for about 15 years -- never have used it.
     
  7. Rudeofus

    Rudeofus Subscriber

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    It depends. One thing you need to be aware of is that AgSO4 is quite water soluble while AgCl is not. So if you for example look at the dichromate bleach in b&w reversal processing, HCl would not work instead of H2SO4. If you pH adjust a C41/E6 bleach which already contains plenty of Br-, Hcl should work as well as H2SO4.
     
  8. KenS

    KenS Member

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    The common household cleaner CLR is dilute Hydrochloric Acid. However... the plastic container does not list it as containing 'hydrochloric acid' but rather as "hydrogen chloride" (HCl) and 'touts' it in their television advertising as being 'environmentally safe'.

    Ken
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    At 31.45%, that is not dilute. Be very careful. That is highly concentrated.

    PE
     
  10. nworth

    nworth Subscriber

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    Sometimes hydrochloric acid can be substituted for sulfuric acid, often not. HCl is usually called for when chloride ion is needed as well as acid. Chloride is pretty active in many photographic situations. Sulfate, on the other hand, is pretty neutral photographically. Another problem is that HCL reacts with a lot of things to release chlorine, which is nasty to both people and photographs. It's better to stick with the acid called for in the recipe unless you really know what you're doing. Incidentally, sodium chloride plus sulfuric acid is often used as a substitute for hydrochloric acid in photography.
     
  11. michael_r

    michael_r Subscriber

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    I don't understand why one would need either Sulfuric or Hydrochloric acid in the darkroom. Other than in some old outdated formulas like Edwal Super 20, when would you ever need this stuff?
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    Reversal B&W bleaches come to mind.

    Glass cleaner for glass plates is another.

    I'm sure I can think of more during the day!

    PE