On Sat, 23 Mar 2019 14:33:48 -0400, you wrote:

>High concentrations of H2O2 result in VERY exothermic reactions. Etching takes place in seconds. Lots of heat. Lots of acrid fumes. Do outside or with a good hood. Have water available to put your board in to stop the etching. I did a lot with those high mixtures but decided it wasn't worth the problems and went back to 3% peroxide. I usually use a sponge with a small quantity of etchant. Takes a minute or two but is very controllable and uses only a fraction of the volume, making disposal much easier. I don't make a lot of boards, so it's not worth keeping vats of chemicals around.

The "top up the solution" is meant to add enough H2O2 to restore the
solution to good operation, but NOT to replace a lot of water.? You
want to maintain the overall concentration.? The goal (I think) is to
maintain the same concentration you get with 3%, but not end up
diluting the overall mixture.? You do lose some to evaporation, etc.

Harvey


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>Mark
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>At 12:32 PM 3/23/2019, you wrote:
>Noted.
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>Thanks,
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>Dave
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>On 3/22/2019 7:40 PM, Harvey White wrote:
>On Fri, 22 Mar 2019 20:31:31 -0400, you wrote:
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>I found Sally Beauty Supply to be a good source for H2O2. I recall the
>"volume" rating is a bit more than 3x the concentration, so "30 Volume"
>H2O2 is 10% concentration.Do be careful, since the drugstore concentration is far less than the
>various products available in beauty supply stores.
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>I'd think that the best use is as follows:
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>1) build the etchant with drugstore H2O2 and HCL.
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>2) when desired, top up the mixture with beauty supply H2O2, but in
>far less quantity than needed for the initial mixture.
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>YMMV
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>Harvey
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