A few days ago I did something simmilar but with 25% aqueous ammonia. I was able to obtain quite intensly colored solution, too dark to see anything
through it unless put directly against a source of light even after diluting it with 2-3 times more water. I used a jar with diameter around 8cm as a
container.
Turns out you can synthesise tetraaminacopper hydroxide electrolytically. With some help of HCl it can be turned into chloride. Obviously due to
strong coloration of tetraamina copper (II) I didn't obtain very concentrated solution.
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