What is the paper, are you sure it doesn't say NaCl? Potassium perchlorate is quite poorly soluable.
Well, to be quite honest. It says NaCl indeed. I asked someone at my university and he said that it doesn't matter for the positive ions, because the chloride is the active part in etching. And he is right about that part.
But (!), I think he didn't realise that the perchlorate is messing things up. He just thought about the salt-part (KCl in stead of NaCl).
Potassium Perchlorate is soluble for 1.5g /100mL I see. So that figures.
I don't quite follow your method, I'd use 17.89g of KCl, add most of the water, add the 1.14g acid and then dilute to 80ml volume. You could also make a stock acid solution at a lower concentration to measure by volume. Are you letting the concentrated acid touch the bare KCl?
I did:
1. Make a 80mL 3M KCl solution
2. Add the perchloric acid (1.14mL & 70%)
But the main problem is the potassium with the perchlorate. It's really stupid that this issue didn't cross my mind. I'm a physics-student, so not quite into chemical mixtures. I only need this to create sharp stm-tips.
I'm going to get some SodiumChloride then. I'll let you know! And thanks a lot for your message!