Making and Using Karat Gold Test Solutions

[lazersteve]

All,

Here's a link to a useful Shor site on making and using karat gold test solutions :

Karat Testing Solutions

Steve

 

[Jim's24K]

Thanks Steve, this link directed me to the answer I needed about testing karat gold. I appreciate your input on the site, and I am learning daily. Happy Holidays to you, your family, and all of the families represented by this site.

Jim

 

[aflacglobal]

Merry Christmas and best wishes to you and yours Jim.


Ralph

 

[peter i]

(Bottle 1) BELOW 14K AND BASE METAL

Mix 10 grams potassium dichromate salts with the 3/~ oz. nitric acid plus ¼ oz. distilled water.

I tried this one, assuming they mean concentrated nitric acid.

It started with a beautiful orange colour, but rapidly grew were dark. Is it supposed to do that?

What is expected shelf-life of the solution?
(I am aware, that AR and its variant in solution 2 and 3 have limited shelf-life too. But how limited?)

It’s working, but seeing a difference between 80%, sterling and fine silver is rather hard to do.

 

[Harold_V]

(Bottle 1) BELOW 14K AND BASE METAL

Mix 10 grams potassium dichromate salts with the 3/~ oz. nitric acid plus ¼ oz. distilled water.

I tried this one, assuming they mean concentrated nitric acid.

I don't know what the site suggests, but you can get far more reliable results by buying a set of test needles and a touch stone when testing gold. Nitric acid, alone, is best for testing most base metals.

I used the Schwerter's solution mentioned for testing silver, and silver alone. As for the formula, the one that comes with the small kit that is available from jewelry supply houses suggests the solution be made with reagent grade nitric, not tech grade. I agree with the distilled water----particularly when testing silver.

It started with a beautiful orange colour, but rapidly grew were dark. Is it supposed to do that?

Depends on what you're testing. If you're testing silver, it depends on the alloy. If you're testing karat gold, I'd suggest it's not worth using. Straight nitric can be useful, however. 14K, for the most part, isn't affected, but 10K will discolor--leaching some of the base metals, leaving behind a dark brown stain (gold).

It’s working, but seeing a difference between 80%, sterling and fine silver is rather hard to do.

The difference isn't apparent initially. After some time, the greater the concentration of copper, the less prominent is the red color.

Mind you, I'm going on memory. I haven't used any of this stuff since '94.

Harold

 

[peter i]

It started with a beautiful orange colour, but rapidly grew were dark. Is it supposed to do that?

Depends on what you're testing. If you're testing silver, it depends on the alloy. If you're testing karat gold, I'd suggest it's not worth using. Straight nitric can be useful, however. 14K, for the most part, isn't affected, but 10K will discolor--leaching some of the base metals, leaving behind a dark brown stain (gold).

Mind you, I'm going on memory. I haven't used any of this stuff since '94.

Harold

Well, I suspect you still have quite a memory, and I’m happy that you are willing to share it.

The funny part is, that it turned dark in the bottle!
Well, There seem to be quite a few different recipes for the Schwerter solution.

Shor: Mix 10 grams potassium dichromate salts with the 3/~ oz. nitric acid plus ¼ oz. distilled water

If the squibble should be “4”, then it might explain my problems

Another source says:
1/2 oz. nitric, 1/2 tsp Potassium Dichromate, 1 oz. distilled water.
I guess this speaks in favour of the squibble-theory.

 

[Harold_V]

I'd agree that it should be 3/4 ounce nitric----but I don't recall the precise amount of potassium dichromate. I may have that information stored in a document I assembled when I sold my refining business.

I am of the opinion that almost any combination will work, but one should standardize how they make their solution, so reactions will be consistent. It helps analyze materials that are in question. Like working with standard solutions.

Darkening in the bottle of the Schwerters solution was common, as I recall. It still worked, it just looked different with time.

Harold

 

[peter i]

Thanks

And I totally agree. Unless you work consequently, remembering to take notes and knowing what you are doing, good results only happen by chance, and are very hard to reproduce.

I keep saying that to young students (and regularly forget it myself when it’s just “a little easy thing”. And later, when a detail made the difference, it’s forgotten.)

 

[LeftyTheBandit]

The gold needles you use with nitric acid, do these needles wear out fast. I'm guessing they are gold plated? A set of these needles appears to cost $50 on ebay and ideas where I could get a set of needles?

 

[Harold_V]

Test needles are not plated. They're made of alloyed gold, with a small piece of each karat fineness soldered to the tip of each specimen. The shanks are made of brass. Each one is marked on the shank as to fineness. The set I used to have had a point that was roughly 1/8" long, made of gold alloy. They were roughly 3/64" thick. Please understand I'm trusting to memory. I haven't seen them in more than 14 years.

They last a long time, even used regularly. The test stone is nicely finished on the functional surface, so it's not very abrasive. A very thin film is wiped from the item to be tested, along with a sample from the desired test needle. How the streaks react to acid determine the karat fineness of the piece in question. The needles generally come with instructions for preparing the necessary acid.

I would suggest to you that if you can buy a set for $50 at today's gold price, you may wish to explore the offering. I have serious doubts that you would receive what you hope for. The exception would be if the tip was much smaller than I recall. It might pay for you to inquire before committing.

A set of test needles should be readily available from a jewelry supply house.
Harold

 

[macfixer01]

Test needles are not plated. They're made of alloyed gold, with a small piece of each karat fineness soldered to the tip of each specimen. The shanks are made of brass. Each one is marked on the shank as to fineness. The set I used to have had a point that was roughly 1/8" long, made of gold alloy. They were roughly 3/64" thick. Please understand I'm trusting to memory. I haven't seen them in more than 14 years.

They last a long time, even used regularly. The test stone is nicely finished on the functional surface, so it's not very abrasive. A very thin film is wiped from the item to be tested, along with a sample from the desired test needle. How the streaks react to acid determine the karat fineness of the piece in question. The needles generally come with instructions for preparing the necessary acid.

I would suggest to you that if you can buy a set for $50 at today's gold price, you may wish to explore the offering. I have serious doubts that you would receive what you hope for. The exception would be if the tip was much smaller than I recall. It might pay for you to inquire before committing.

A set of test needles should be readily available from a jewelry supply house.
Harold

Note to Steve,
I for one would sure like to see a gold testing video, it would be worth buying. Reading descriptions isn't the same as seeing someone do it the proper way and knowing what kind of changes to epect. I bought some testing supplies on Ebay (stone, test solutions, magnifier, needles). Had it sitting around for a couple months before I tried to use it so likely the acids are bad maybe? Anyway even with hallmarked items I wasn't getting the kind of conclusive results I hoped for. It just seems like there is maybe some skill involved also?

macfixer01

 

[Harold_V]

You will achieve mixed results with a touch stone. The strength of the streaks tends to vary, but as you use the system more and more, you will become more familiar with the process. The worst thing you can do is use it only when you need it. Practice repeatedly until you are familiar with the reactions, and how to create the streaks.

I found I achieved the best results if I made streaks that were well above and below the one I was testing. If you think you're testing 14K, make a 12K and 16K streak, with the questionable streak in the middle. When you apply the acid drop, watch which one dissolves first. Start with plain nitric if the karat is low-----use the AR mixture only for high grade streaks.

Practice------then practice some more.

Harold

 

[Pawnbroker Bob]

I just posted The Pawnbrokers Guide to Testing Metals pdf in the book section. This was published in this months Todays Pawnbroker magazine.

Distructive and non distructive methods of testing all precious metals with acids and solutions.

Enjoy!

Pawnbroker Bob