Stannous chloride test solution is one of the most important tool and a most have for any precious metal recovery and refining process, this test solution will tell you if there is presence of dissolved precious metals (gold, platinum and palladium) in a solution or not.
On this article we will go over: how to make by your self Stannous Chloride test solution, testing principles and show how test results should look like.
Making Stannous Chloride test solution:
Place 2 grams of pure Tin powder in an eye dropper bottle and Dissolve it with 30 ml of hydrochloric acid 32 % (HCl). You can give it a short boil to get the reaction going or just let it react at room temperature, when stop fizzing & bubble and cooled down your Stannous chloride test solution is ready to use. You can change the proportions if you like, the main idea is to dissolve the Tin with the HCl and remember those proportions since you will acquaint yourself to the different results later in this guide.
If you can't get pure Tin powder, you can use high Tin percentage solder and you may need to add a bit more metal to dissolve in the acid. Once your test solution is ready it should be clear and colorless and when not in use, the eye dropper bottle should be sealed and stored in dark and dry place.
Alternatively, you could purchase dry Stannous chloride (SnCl2) salt and dissolve about 3.2 grams in 30 ml of hydrochloric acid 32 % (HCl).
Stannous chloride test solution doesn't last forever and have a shelf life of about 3 -5 weeks before it start to decompose and show test results slowly and even false readings, we recommend to replace the test solution every 3 weeks.
"In solution" – What is that?
Stannous Chloride test will help you test for precious metals that have been dissolved in acid solutions, much like sugar that have been dissolved in water. It will not work on elemental metal such as powders or jewelry piece. Stannous Chloride is practically your eyes for that matter, to look into a solution and tell what's in a liquid, We can't stress enough the importance of this test for the recovery and refining process of gold, platinum and palladium.
A few basic rules and procedures to follow will ensure you the right results every time.
First and foremost, acquaint yourself by testing known Gold, Platinum and Palladium solutions at different levels of concentrations, this will help you determine in the future what precious metals are in the solution and approximate how much of it is actually there. Always use fresh test solution, and use the same proportions when making new test solution.
Perform test on a white surface such as Spot plate, Filter or Q-tip. Never test a solution with excess oxidizer in it, it will affect the test and might yield false results.
Usually one drop of the "suspected" liquid and one drop of test solution is sufficient to yield immediate and reliable results.
Concentrated Gold solution (left), diluted 4 times over with water (center), diluted 10 times over with water (right):
Notice the deep purple almost black. The gold purple stain will not disappear at all from the test surface while drying.
Concentrated Palladium solution (left), diluted 4 times over with water (center), diluted 15 times over with water (right):
Notice the rainbow like effect, main color with Pd is green. Palladium test stain will dissipate after a few hours.
Concentrated Platinum solution (left), diluted 4 times over with water (center), diluted 10 times over with water (right):
Notice the deep beautiful orange color almost brown.
False Positive for Gold
Sometimes different material complexes may fool our test solution. This is the most common of false positive of them all is a combination of Sulfurous acid and Copper chloride.
Here we simply dissolved a tiny piece of copper with Aqua-Regia, added SMB (sodium metabisulfite) and swabbed it to test with Stannous Chloride.