When you mix the salt (sodium chloride, NaCl) with vinegar (5% acetic acid, HAc),\ufffd the result is\ufffd weak homemade hydrochloric acid (HCl) and some leftovers.\ufffd It's slower because it's weaker, and needs replenishment as the Cl ions are used up in the etching reaction (more salt = more Cl ions). Might as well start with the pool muriatic acid (HCl), admittedly stronger than the vinegar/salt, since that's what you wind up with anyway, just weaker.\ufffd Beauty shop suppliers will have higher concentration peroxide in quart bottles for reasonable prices. Their concentration is measured by 'volume'\ufffd -\ufffd typically,\ufffd 40 volume = ~12%, IIRC, so use 1/4 as much as the 3%.\ufffd The overall solution will be stronger, since there is less water than using the 3%. You just use less of the higher concentration peroxide.\ufffd\ufffd Both the pool acid and higher concentration peroxide are quite caustic/corrosive, and need to be treated with real care and respect.\ufffd Rubber/plastic apron and gloves, safety glasses!\ufffd Ventilation!\ufffd And don't use it (or ferric chloride, for that matter) around your tools - the vapors from an exposed etch tank will leave a nice rust patina on the iron surfaces!
If you can find it, Sechelle had written an excellent article on
CuCl etching, explaining the chemical process.\ufffd It seem to have
disappeared from it's old internet sites.
Norm
\ufffdI\ufffdm trying to wrap my head around how this works, to better mix it.\ufffd I actually like working with this method \ufffd the resulting etchant is way less unpleasant than ferric or the HCl/peroxide stuff.\ufffd It is way slower, although I\ufffdve found adding peroxide/salt seems to speed things up a bit.
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The only negative I\ufffdve found is that peroxide typically is only available in small 300-500ml bottles, which depending on which store you raid cost anywhere from $1.99 to $3.99 CDN each.\ufffd And you kinda get weird \ufffdis this guy a terrorist?\ufffd looks when you check out six or eight of em at a time.\ufffd I\ufffdve looked around for \ufffdbulk\ufffd peroxide but have only found industrial stuff that is at 32% (vs 3%).. wondering how that would change things in the reaction?
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I\ufffdm also wondering why it seems like I can keep the reaction going indefinitely if I constantly intervene to stir, add a bit of salt, add peroxide, etc.. but once I let it go it cannot be restarted again.\ufffd Also curious why sometimes I get a blue coloured etchant at the end, whereas other times I get this foamy, nasty green.
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I\ufffdd love to figure this out more and refine it.\ufffd The real obstacle is the cost and small quantities available of peroxide.\ufffd I\ufffdd love to find a way to buy that that doesn\ufffdt leave me feeling like a weirdo.\ufffd J
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Brad
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