Higher ct Acid Solution? ratio needed....

[davewilson24]

Hi im trying to mix up a batch of 14-22ct testing solution using nitric acid and hydrocloric acid. iv gone with the Aqua regia mix of nitric 70% 1:3 hydrocloric 28%. This does react with the 18ct hallmarked gold im trying to calibrate the acid with, however it takes 20 seconds.

So heres the big question. how to i speed the reaction up so it falls into the the 3-10 seconds reaction time, like the mix purchased from shops.

im just not to sure about mixing the acid in random ratios.

iv also got distilled water if this is of any use.

many thanks in advance. cheers

 

[butcher]

I would just mix aqua regia and use karat needles and stone.

try searching for pawnbrokers guide to metal testing.

 

[davewilson24]

Hi cheers for the reply. Iv had a play with diffrent mixtures now. Iv found that 2 parts nitric acid at 70% and 3 parts hydrocloric at 28% works perfect. The acid turns yellow as expected whenplaced on 18ct gold. This happens at 6 seconds. Perfect, as the shop product guide is 3 to 10 seconds. Hope this helps someone. Cheers

 

[autumnwillow]

Dave,

Thank you for sharing the 2 parts HNO3 to 3 part HCl it worked great for me rather than the 1:3 ratio.

Just one question, are you judging the assay based on the color of the acid? Not the color of the scratched gold on the touchstone?