Storage and shelf life, Schwerter's solution.

[qst42know]

What is the shelf life of Schwerter's solution?

This is the second time I bought silver test solution from a jewelers supply house and get no red reaction on known silver.

Could it be their stock is old or stored improperly?

 

[rusty]

Your nitirc acid may have gone a bit stale, I doubt that the potassium dichromate would go bad. Add a small drop of nitric to freshen it up.

From Hokes book, Testing Precious Metals

Here is another way to establish silver: In another bottle mix up nitric acid and a few crystals of potassium dichromate.

Place a drop of this solution on the suspected article (after getting rid of lacquer, etc.) and note the color effect. Silver will show a very
strong, definite red, through the formation of silver dichromate.

 

[FrugalEE]

The bottle I bought back in November of 2010 still gave me a good reading this afternoon. I got it as part of a Gold testing kit.

 

[lazersteve]

Make sure your silver is bare and not plated with Rhodium or covered with flux if you melted it yourself.

My silver test solution is several years old and still works fine.

Steve

 

[qst42know]

After some testing I would guess this to be a very weak solution. After a prolonged test on a US 64 quarter I had to use a loop to see the tiny red dust specks.

It seems to etch well enough based on the fizzing but may be short on dichromate as I'm not getting much of a red indication.

 

[butcher]

Could you evaporate down to crystal salt add some HNO3 to concentrate it?

 

[qst42know]

Butcher

Reconstituted sounds like a viable idea, with the exception of this is only a 1/2oz test bottle. I see potassium dichromate is reasonably inexpensive for a life time supply. If I make it myself then I can know it's right.

 

[butcher]

I want to make my own K2Cr2O7, then make schwerters from that, it doesn't seem too involved. now Hmm the truck bumper, or stainless steel?

http://www.chemguide.co.uk/inorganic/transition/chromium.html

http://www.public.asu.edu/~jpbirk/qual/qualanal/chromium.html

http://webpages.charter.net/dawill/tmoranwms/Chem_Chromate.html

http://www.erowid.org/archive/rhodium/chemistry/potassium.dichromate.html

maybe Tim W. could give some pointers?

 

[lazersteve]

Please be very careful with chromate solutions as they are very hazardous.

Steve

 

[butcher]

Thanks Steve, Great advice as always, I would not attempt before much study, one reason I have not done it yet, I am still studying projects started last year. It Seems like I can make a career out of studying one thing.

 

[qst42know]

I had thought this test solution was short of potassium dichromate, however on an unmarked piece of suspected silver I put one drop of 10k test acid (dilute nitric) and allowed it to work all it would. To the same spot I added a drop of the suspect silver test solution and sure enough the spot turned blood red.

Rusty was correct the nitric portion of this solution has weakened somehow.

 

[goldsilverpro]

I would guess that the small bottles of Schwerter's contain weak nitric to begin with. If they were straight nitric, they would probably require Hazardous shipping. Hoke's instructions seem to use straight nitric.

The last time I made this, I used the K2Cr2O7 that came with a testing kit. If I remember right, it said to add the 10 grams of K2Cr2O7 to about 50 ml of HNO3. I used the same solution for several years. I just bought a pound (several lifetime supplies) on eBay for about $10.

Search for Schwerter's in Harold_V posts. BTW, is that spelling right?

 

[qst42know]

Search for Schwerter's in Harold_V posts. BTW, is that spelling right?

Don't ask me if anything is spelled correctly I rely heavily on a spell check crutch. :lol:

The wiki on potassium dichromate points to an approximately 35% nitric to make Schwerter's solution. It's interesting they would specifically mention approximate :?: . Certainly the person credited with the discovery had a formula in mind?

I suppose the important conclusion is to test your test solutions against known values before you trust them.

 

[FrugalEE]

There are two forumals for making Schwerter's in the General Reaction List along with a rather long list of the various color reactions.