Gold and silver testing acid

[Yef]

Dear Sir,
Can someone help me for exact formula to make testing acid for gold 18k and 14k.
I tried many times using commercial HNO3 and HCl acids. But in vain.

Thanks in advance.
Yef

 

[nickvc]

I’m fairly sure if you have known pieces you can create your own , I’m fairly certain it’s different strength aqua regia , the lower the oxidizer , nitric , level the more resistance high carat pieces will have, you could even try diluting a standard AR solution to see if that works.

 

[adam mizer]

I had problems figuring out what you guys meant. The formulas are in fluid ounces, not weight ounces. There are 29.6 mL in a fluid ounce. I just copied it off the instructions. Please not that I have never mixed these up. I always used the various pre-mixed solutions that I bought from companies that sell jeweler's supplies. I also see them on eBay. They also have 22KT. They're cheap.

If you can measure mL, milliliters, that would be the easiest. Here are the exact numbers. You can probably round them off. Just measure them as accurately as you can. Fluid ozs. don't convert to mL that evenly.

10KT - 22.2 mL nitric - 7.4 mL distilled water
14KT - 23.7 mL nitric - 5.9 mL distilled water - 10 drops hydrochloric
18KT - 5.9 mL nitric - 5.9mL distilled water - 17.8 mL hydrochloric
Silver - 20 grams potassium dichromate - 22.2 mL nitric - 7.4 ml distilled water

I found this old post from goldsilverpro.

EDIT: should have inserted the link, the 14kt is questionable and was answered as 5ml.
https://goldrefiningforum.com/threads/making-gold-testing-solution.311/#:~:text=When you apply the acid to the streaks

I believe based on Technical or Reagent grade Nitric.

 

[Yef]

I found this old post from goldsilverpro.

EDIT: should have inserted the link, the 14kt is questionable and was answered as 5ml.
https://goldrefiningforum.com/threads/making-gold-testing-solution.311/#:~:text=When you apply the acid to the streaks

I believe based on Technical or Reagent grade Nitric.

Many thanks Adam.

 

[adam mizer]

Your welcome.
Oh.... the basic HCL used here in the USA is 31.45%

 

[tmj883]

How to Test Gold, Silver and Other Precious Metals.​

To start, make three test solutions as follows:​

1. Bottle #1: Schwerter's Testing Solution - Mix 1 gram of Potassium Dichromate with 22ml of concentrated Nitric acid and 8ml distilled water.
2. Bottle #2: Mix 1 part (by volume) Hydrochloric acid and 50 parts of Nitric acid. Add to 12 parts of distilled water.
3. Bottle #3: Aqua Regia - Mix by volume - one part Nitric acid to 3 parts Hydrochloric acid. Caution!! Aqua regia is highly corrosive. Freshly prepared it is colorless, but turns orange within seconds. It decomposes rapidly so only mix a small batch for testing.

GOLD TESTING​

Pure gold is very soft. To make it more useful it is hardened by alloying it with other metals. Pure (or fine) gold is 24 carat; 14 carat is 14/24 (58%) gold by weight, the balance an alloy metal.

Test to distinguish gold from non-gold:

• File a notch in the piece to be tested.
• Apply a drop from Bottle #1

Results:

A bright green reaction indicates gold plate on copper or brass. A pinkish cream color indicates gold plate on silver.

Test to distinguish gold carat values:

• File a notch in the piece to be tested.
• Apply a drop from Bottle #1. Ten carat gold will show a slight reaction, over 10 carats, little or no reaction.
• Apply a drop from Bottle #2. Fourteen to 18 carat will show a slight reaction, over 18 carat, little or no reaction.
• Apply a drop from Bottle #3. Over 18 carat will show a slight reaction.

SILVER TESTING​

Pure silver is almost perfectly white, and very malleable. Because pure silver is too soft for practical use it is usually combined with copper to harden it. Sterling silver is 92.5% silver and 7.5% copper by weight. Mexican silver is typically less than 90% pure silver.

Test for silver:

• File a notch in the piece to be tested.
• Apply a drop from Bottle #1

Results:

• Pure silver turns bright red
• Silver (Stirling Silver 92.5%) turns dark red
• Silver (80%) turns brown
• Silver (50%) turns green

OTHER METALS​

Using Bottle #1 and above procedure look for the following reactions.

• BRASS - Dark brown
• COPPER - Brown
• NICKEL - Blue
• LEAD - Yellow
• TIN - Yellow
• PALLADIUM - None

 

[Mech]

Is there a self life to these , and how long is it good ?

I have been using one of the major brand kits , do not remember - I thought someone mentioned a shelf life for those kits also ?
There were 5 bottles , one for silver and a touch stone .

 

[FrugalRefiner]

Yes, they will all deteriorate over time. How long depends on storage conditions like temperature, light, exposure to oxygen, etc.

Dave

 

[Yef]

I found this old post from goldsilverpro.

EDIT: should have inserted the link, the 14kt is questionable and was answered as 5ml.
https://goldrefiningforum.com/threads/making-gold-testing-solution.311/#:~:text=When you apply the acid to the streaks

I believe based on Technical or Reagent grade Nitric.

Hi Adam,
Thanks for your reply.
I just tested the formula for 18k you sent but both 18k and 14k disappear.
Maybe I should test with less Nitric acid?
Regards,
Youssef

 

[adam mizer]

Hi Adam,
Thanks for your reply.
I just tested the formula for 18k you sent but both 18k and 14k disappear.
Maybe I should test with less Nitric acid?
Regards,
Youssef

I have never used the formula's however.
If the scratch disappears I would try 12kt or 10kt.

Also if I were to make these test formula's, I would personally have new JSP acid test bottles to verify that my acids are working correctly.
The karat gold also needs to be a fixed and verified amount in order to make the proper acid mixture.
This would tell me that I would be mixing the correct ratio of acid.

I wonder about acids we purchase, they state a certain percentage, but the purchased acid could have been stored incorrectly and aged.
Like my recent purchase of Muriatic acid, was a very amber color and I searched for possibly a date code.
Found some digital numbers on jugs and sort of appear like made in 2023.
Kinda tells me my acid is not fresh and new.

 

[FrugalRefiner]

Hi Adam,
Thanks for your reply.
I just tested the formula for 18k you sent but both 18k and 14k disappear.
Maybe I should test with less Nitric acid?
Regards,
Youssef

Given enough time, "18K" test acid should dissolve most gold. It is aqua regia, and we use it to dissolve gold all the time.

The key to using these test acids is using a stone and test needles of known karat. Scratch the unknown object on the stone. Scratch a test needle of higher karat on one side of the unknown's scratch and lower karat on the other side of the unknown object's scratch. Apply the test acid to all three scratches at the same time, then watch them as they dissolve. The lower karat scratch should dissolve first, then the unknown, and finally the higher karat. It's the relative time to dissolve the scratches that's important.

Dave