At 5/6/2022 04:43 UTC Morris Odell wrote:
Thanks Jim,
I added about 3 cm of thick fine-stranded copper wire to my 700 ml of solution and left it overnight with the air pump going. The next morning all the copper had dissolved but the solution was quite dark, indicating that the copper (1) had not been oxidized to copper (2).
To me this means you had some available Cu(2) to dissolve the copper wire, but not enough free HCl to allow 2 Cl ions for each Cu, therefore much of the dissolved copper was in the form of Cu(1)... dark brownish and insoluble.
When it comes to the concentration of copper in the solution, my recipe for making an initial solution calls for about 200 grams (7 ounces) of copper to make a liter of solution. That's about 14 feet of #10 copper wire... 22 feet of #12... 36 feet of #14... 56 feet of #16. That's the generally recommended concentration of copper in the working solution. The 3 cm was a really good test of the problem... no free HCl. Now you need gauge whether you have enough copper. You'll have to do that based on your memory of how much was used to make the solution in the first place.
I added 10 ml of concentrated (pool chemical) HCl and there was some improvement after another night. I added another 10 ml of HCl and now it looks terrific.
Exactly what you needed. Good job!
I tested a tiny sample with a few drops of 6% H2O2 and there was no change, which I think means that oxidation using bubbled air was complete.
Yes. But 10 ml (a bit over 1/3 oz) is a pretty small amount of HCl depending on the total volume of solution... and some of that already went to form CuCl2 so you still don't have much excess... meaning that after not too many etches you might quickly get back to a muddy brown solution you can't rejuvenate just by bubbling. I like to have about a liter (bit over a quart) of solution - although I don't use all of it when etching - and if my solution were acting like you describe I'd add at least one, maybe two, ounces of 37% HCl. That's for a liter of solution. More or less depending on how much solution you have. It shouldn't make for enough excess HCl that you have to worry about fumes.
I'm going to try etching a small piece of board to see whether it can stay oxidized but I won't have time to do that for another couple of days due to other commitments. It does seem that the fix was to make sure there was enough HCl present. I don't have a pH meter but I imagine that one would be quite useful.
The slight excess of HCl was the key in your case.
You don't need a pH meter. Just take a bit of dry baking soda... Arm & Hammer Bicarbonate of Soda is one brand... and add a few drops of solution to it. If it bubbles fairly vigorously you have excess acid (HCl). And if it doesn't have a strong smell you don't have too much HCl.
Yes... please let us know how a trial etch turns out.
JimH
