Bruising/pitting in 9ct gold

[LeighnaKing]

Hi everyone

I've recently started to play around with 9ct yellow gold, and just finished this little opal ring and stacking band. I'm pretty happy with it, but after taking the attached photo, I can see a lot of bruising/discolouration and pitting. Don't get me wrong, I quite like the effect (I'm after the organic/unearthened treasure effect) but if it's causing the gold to be weak/brittle, then I need to work out what's causing it. I'm entirely self-taught, so am certain it's something I'm just doing wrong. Could it be overheating the metal too much?

Any help or advice would be much appreciated

Thank you!