This is just a guess, but that is what others seem to be doing too.
From the description (solid powder, clear solution becoming colored but still clear) it is probably a "per"xxx something. Persulfates are common, like ammonium persulfate and sodium persulfate.
The ringer is the white solid precipitate at the end of the etch. Now, that can be done with a second step to precipitate either the sulfate (e.g., add calcium or barium hydroxide), or one can precipitate the copper and get a slightly green (usually) powder. But, the description implies a second step is not necessary.
I was thinking it might be one of the so-called "solid hydrogen peroxides." The percarbonates or perborates would fit into that category. The percarbonate would be interesting as that would leave copper carbonate as an insoluble powder. Problem is, I am not sure it will etch under alkaline conditions. Under acidic conditions, the copper (II) would most likely be soluble. Borate is a different story. I couldn't find after a brief search the actual solubility of copper(II) borate, but it precipitates from water solutions readily. (Copper(I) borate is reportedly soluble in water.)
So, taking everything that was stated as true, including the statement that the solution it is mildly acidic, I would guess it maybe a soluble perborate salt and may have a little free boric acid present. A percarbonate salt is another option, but doesn't account for the acidity. If sodium phosphate were present, the precipitate might be copper phosphate. That might solve the solubility problem with any of the "perxxx" type of compounds. The white granules being sold many be a mixture to account for all of the described properties.
John
----- Original Message -----
From: David
To: Homebrew_PCBs@yahoogroups.com
Sent: Sunday, September 23, 2012 11:23 AM
Subject: [Homebrew_PCBs] Etchant Identification
Hi All,
Can anyone tell me what this etchant is? I have not seen such before.
http://www.ebay.co.uk/itm/1pc-Copper-clad-palte-CCL-PCB-blue-environmental-protection-etchant-200g-/251130218053
Thanks,
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