The pure acid's stored in a proper cabinet will change in time
aswell. Do you refresh them every day aswell? Are they degrading
thismuch in a day, I don't think so.
No, I do not change my acid every day, and you are correct about
electronic gold testers. I bough one and I never use it, precisely
because the accuracy depends on acid concentration.
I guess the best way to answer is to describe how I was taught to do
I have 5 needles in my kit - 22k, 18k, 14k, 9k, 6k To do the test I
would do 5 parallel streaks with metal under testing. Below these 5
streaks, I would do 5 streaks, one with each needle. Acid applied
across both groups of streaks in one swipe per group, let dry,
gently washed, and examined.
Even if acid weakens, the needles give you a basis for comparison.
Without needles, you are relying on memory, but what cannot be
possible known is how the acid changed, since reaction was memorized.
As far as refiners, gold purchases, and etc… They simply protect
themselves by under-paying. It is more efficient for them and in a
long run they come out ahead. Even if some customer may ask a
question, they have plausible explanation for their practices. Very
few know exactly what is in their scrap and go to the trouble to