That’s terrible, it seams to me that the basic casted ring has had a
brittle matrix with big crystals.
You can have made two mistakes. The gold alloy was overheated and
oxidized before poring . Some of the copper in the gold has become
copper oxide and moved to the crystal edges of your alloy. this gives
a brittle alloy. If you throw this hot into pickle the copper oxide
will solve so fast that there will be high internal tensions on
crystal level. This gives the cracked surface, direct or later on.
To prevent this happening use an reduced flame when you are using gas
and oxygen.( an overdose of gas). and use and anti oxidant as some
charcoal in the melt and cover it with some borax. Also some sugar can
be used, contains a lot of carbon and sticks good to the surface. And
keep the flame always covering the gold surface during casting work…
You can use the gold again but stir it when liquid(egg face) covered
with an borax sugar mixture. so that the oxide gets out.
The second thing what could happened is, when soldering and the
material is heated for a long period, there will be a crystal grow.
Also when you overheat the object during soldering without protection
against oxygen , this will help the copper oxides creeping in. And if
you are using an oxidizing flame you ask for it.
So it seams to me that the copper oxides have solved in the pickle,
and left no binding over between the gold/copper crystals. And if there
are internal tensions in the ring it will crack.
Good luck in doing at again. (And as you know, the second time always