I agree with the theoretical renditions of my colleagues.
I also suspect that there may have been a reaction performed by Glace using his prepared cupric chloride (which likely had a high chloride concentration and was in contact with copper metal at some point), which eventually strangely appeared to produce a precipitate.
I explain my presumed formation of what I surmise is copper oxychloride as a result of a comproportionation reaction from the action of copper metal acting on cupric chloride (see https://en.wikipedia.org/wiki/Copper(I)_chloride ) in the presence of a high chloride concentration creating a soluble CuCl2- complex:
Cu(ll)L + Cu <--> 2 Cu(l)L (L here refers to a chloride ligand)
So Glace’s starting solution could have been a mix of complexed cuprous plus cupric chloride.
Of note is that there also exists an equilibrium reaction between water and the aqua cupric complex providing an acid source:
[Cu(H2O)6]2+ (aq) + H2O (l) = [Cu(H2O)5(OH)]+ (aq) + H3O+ (aq)
The final piece of the puzzle is the electrochemical reaction consuming the created H+ (moving the above equilibrium to the right) activated by the oxygen in air in the presence of cuprous:
4 Cu+ + O2 (from air) + 2 H+ → 4 Cu2+ + 2 OH- (source: Wikipedia reference above and also Eq (7) below)
A related reaction also occurs with ferrous, oxygen and a souce of H+ (see https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/html/final-78.html ).
Here is an extract from Wikipedia (see https://en.wikipedia.org/wiki/Dicopper_chloride_trihydroxide ) on the reactions associated with the preparation of copper oxychloride:
“ CuCl2 + Cu + 2 NaCl → 2 NaCuCl2 (eq.6)
6 NaCuCl2 + 3/2 O2 + H2O → 2 Cu2(OH)3Cl + 2 CuCl2 + 6 NaCl (eq.7) “
where Eq (6) produces a soluble cuprous complex which feeds Eq (7), an electrochemical reaction.
Copper chemistry can be a bit surprising at times.