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Holt
06-01-2002, 09:00 AM
Is there a quick "at-home" test for the element gold?

Holt
06-01-2002, 09:00 AM
Is there a quick "at-home" test for the element gold?

Tom McIntyre
06-01-2002, 02:54 PM
It depends on what kind of acids you keep at home. Strong Nitric Acid will dissolve and metal besides gold resonably quickly. The normal test is the rub the metal on a piece of slate and then drop some acid on it. If it changes color, it is not gold.

An easy and pretty accurate test is to just taste it. Most metals that look like gold have a coppery taste while gold is tasteless. (Most of my friends find this test tasteless also, especially when they see me licking watch cases :biggrin:)

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Tom McIntyre
Past President, NAWCC Chapters 174 and 87
Member Chapters 8, 87, 149, 159, 161 and 174
NAWCC: Crafts Committee, Web Committee
Pocket Horology Web (http://www.pocketwatch.org)
Tommy the JOAT's Web (http://www.AWCo.org)

jagkar
06-01-2002, 03:48 PM
A jeweler once told me that most gold imitations will react to common household bleach, gold will not. After a while you can just recognize the various colors of gold almost 100% of the time. The nitric acid test above is the Cadillac test, tho. Again, with practice, you can even estimate the carat content by the rate of reaction with the nitric. Specifically no reaction at all with 18k, very minor with 14k, definite reaction and bubbling with less than 10k etc. Also stuff will clear up sinuses.

Holt
06-01-2002, 05:55 PM
Thanks Tom, I tried the taste test on several items around the house. (Easy!)

I did figure out,that this "taste-test" it is not reliable if you have recently handled copper. the copper can still be detected by smell on your fingers and will give a false-positive, as it were.

Jagkar, I will play with the bleach thing tommorow and see what happens,

I didn't understand the nitric acid test, do you rub the gold on the slate, and test the slate, or do you rub the slate on the gold and test the gold?

Holt

Steve Maddox
06-01-2002, 08:45 PM
Holt,

The test Tom described is called a "touchstone" test, and it's been used for generations. Basically, you rub the article to be tested against a stone (slate, novaculite, etc.), so that it leaves a metal mark on the stone (like an aluminum pot or pan will on a white porcelain sink). Then, you apply a nitric acid solution to the mark, and observe the results.

Most "acid type" gold testing kits come with a set of "needles" that have solid gold tips of various known karats. To get a good idea of the karat of an unknown gold, one would make a mark on the touchstone with the gold to be tested, and additional marks with the testing needles. The approximate karat of the gold being tested can be determined by observing how similarly it's mark reacts to those of the known karats. Lower karat gold will be dissolved more rapidly, so that if 14k and 18k testing needles are used, and the mark from the unknown sample dissolves more rapidly, it's safe to conclude that the unknown sample is lower karat than the known examples. On the other hand, if the mark from the unknown sample dissolved after the mark from the 14k needle, but before the one from the 18k needle, it would be concluded that it's karat was somewhere between.

Unfortunately, many who are, shall we say less than skillful, dispense with the touchstone and the needles, and just apply drops of nitric acid directly onto the article to be tested. If it's not solid gold, a violent reaction will result, which causes oxygen bubbles to be released. If the item IS gold, however, a far less violent reaction will occur, proportional to the karat, but it will still result in the gold becoming etched and discolored unless it is extremely pure (approximately 22 karat or higher), and the acid is removed fairly quickly.

Obviously, gold testing acid will very quickly RUIN a watch movement, and it should never be applied to a case with a watch inside it!

As a (perhaps) interesting side note, one of my old jeweler friends who was in business during the Great Depression, said that people used to drag all sorts of "gold" stuff in to sell for scrap. Of course, he knew that if the item said "gold filled" or "guaranteed xx years," it wasn't solid gold, and didn't warrant any further investigation, but he said many of his customers expressed doubt. On a whim one day, when a customer questioned how he new a particular item wasn't solid gold, he put it to his nose, and sniffed it. He had a big nose, and the customer was satisfied that he could tell the difference by smell. After that, whenever he had to "test" whether or not something was solid gold for a customer's benefit, he'd use the "sniff test," and he said not a single customer ever questioned it.

Man! All these cool stories I've heard from days gone by -- maybe I should write them all down somewhere! :biggrin:


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Steve Maddox
President, NAWCC Chapter #62
North Little Rock, Arkansas

Jeff Hess
06-02-2002, 04:05 AM
Please be careful with destructive test on gold watch cases.

I urge you to familiarize yourself with gold cases of everykind. Study ALL the available material for hallmarks, makers marks etc. Tom M. 's golden "tongue in chic"
(heh) suggestion has much merit. IF you handle, touch, smell, and gently squeeze a few thousand cases, you will be able to discern 99.9% of gold cases against non gold. Gold has a feel, a look, a tarnish, a smell that non gold does not. And if you find one of those MINT Ladd 30 year cases that DO, on occasion, befuddle you, just give the case a "slight" bend. (No, don't BEND the case, just tweak it, press it gently.) This will usually tell the tale. Do NOT use acid on a watch case. I implore you.
This is a mjor bugaboo of mine (feel free to flame me...) but I think dropping acid on a watch case (other than one that is in the scrap heap) is not only counter productive, sometimes requiring BUFFING to repair the resulting damage, but also inviting disaster from leaking acid onto movements (sometimes the tiniest acid residue will permeate to a movemnt and mess with the gilding). Acid is also very bad for you. And a scratch test, even scraping a case lip, does take away from the case and make a flat spot on the case. (Sure, it is minute, but think of the damage of this being done scores of times over the life of the case. And even the karatage of gold is pretty easy to figure out just by the color.
Try it. OK, let me have it...flame away! JPH

abereiter
06-02-2002, 04:31 AM
How does the taste test work on "minty" cases? :biggrin:

Barry G
06-02-2002, 04:45 AM
I've had good luck with an electronic gold testing kit that does not involve the use of acid. The tester has a small resevoir or well at the bottom of which is a tiny piece of 24k gold for reference. You mix a few drops of testing solution into the well, attach a wire to the item to be tested with a small alligator clip, and dip the item into the well. The attached unit then lights up to tell you whether the item is gold and, if so, what karat.

I have tested this unit on known samples [e.g., hallmarked cases] and gotten good results. On a rare occasion I will get a false positive on a heavily gold-filled case [it will register as 10k gold], but that is also a problem with using acid unless you want to scratch through the gold-fill to the expose underlying brass.

I've carried this unit with me to antique shows, and it fairly easy to set up and use. It's not as dangerous as fiddling with acid, and since it doesn't damage the case dealers don't seem to mind if I want to use it to test out a questionable item.

Regards,

Barry

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My Online Pocket Watch Collection (http://barrygoldberg.net/watches.htm)

Jeff Hess
06-02-2002, 04:54 AM
Barry is right again.
We have used several of these elecrtronic testers over the years. the first ones used ACID. We just got the latest one friday and it uses something akin to vinegar. And it WORKS. Will share the name of it when we get into the office Monday. If you MUST do this stuff use an electronic tester.

Jeff Hess

Jeff Hess
06-02-2002, 04:59 AM
As an amusing aside..there is a major coin shop in our area. They use a dremel tool or file and acid on EVERYTHING that comes into their shop.

The big joke here is when a few of us collector/dealers get together trading stuff and someone pulls out an 18th century silver box or a 1940's pocket watch we can often tell the origination of the piece.

"Oh, you got that from XXXXXX Coins?" "How did you know?" Heh. the telling signs are acid burns and grind marks on pretty signifecent stuff. Even railroads marked 25 years! Sheesh. LOL. Jeff H.

Barry G
06-02-2002, 05:00 AM
The electronic gold tester I have is made by "RS MIZAR". I found it for sale on-line by doing a search on "electronic gold tester." They come in a variety of styles and costs, and I got the "el cheapo" model for somewhere around $100. the main differences in the models is how accurate the testing is. Mine can only distinguish among non-gold, 10K, 14K and 18K, which is fine for my needs. The more advanced models can distinguish among 9K, 10K, 12K, 14K, 16K, 18K, 20K, 22K and 24K.

Barry

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My Online Pocket Watch Collection (http://barrygoldberg.net/watches.htm)

Holt
06-02-2002, 05:01 AM
I would never use the acid near a watch movement, this question came to mind when I recieved an antique watch chain in the mail, from a seller who had advertised it as "gold filled". The chain and "T" showed no evidence of wear, just a slight "tarnish". It was at that point, thinking the seller may have sold me a solid gold chain with no marks, that I wondered if there was a quick at-home test you could use to tell if it was gold, or not, if there was no sign of wear. (ie. plate, rolled, or filled)

Purchasing and learning how to use the gold test kit, would be the way for me to go, but even that is a little out of my league for now, I pretty much know by the quality, and price of what I can afford to buy, whether or not it's gold!

Holt

Holt
06-02-2002, 05:07 AM
Scratch that(I love puns) remark about the acid kit being the way for me to go, I like the sound of the electronic tester much better!!

Holt

Tom McIntyre
06-03-2002, 02:51 AM
Maybe I will get me one of those electronic testers. As I get older my tongue is losing sensitivity.

As for a "false positive" reading of 10K from a gf case, the Ladd cases are actually 5K on the 30% gold ones and some of those will go rather higher with the solid gold reinforcement at wear points. I value Ladd cases as the same as 9 karat.

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Tom McIntyre
Past President, NAWCC Chapters 174 and 87
Member Chapters 8, 87, 149, 159, 161 and 174
NAWCC: Crafts Committee, Web Committee
Pocket Horology Web (http://www.pocketwatch.org)
Tommy the JOAT's Web (http://www.AWCo.org)

Dr. Jon
06-03-2002, 06:17 AM
YOu asked for quick and dirty. I go by feel and heft. Witha bit of practice you can get a quick and usually reliable impression by pressing on the inner dome.

Knowledge of hall marks is also useful and quick.

I may be ignorant lucky or both but I have never had a hall marked case give me reason to doubt its correctness.

I have seen some base metal cases marked 18 carat gold so I don't trust that.

If it is gold it is almost inconceiveable that it won't be marked. The only possible exception that I would consider is if the case looked handmade by an amateur goldsmith, and that is easy to spot

Holt
06-03-2002, 06:48 AM
My question was in regard to an antique watch chain, that had replacement "T" bar, rings, and clip, which were all easily identified as "gold-filled". The remaining chain showed no signs of wear, leading me to wonder if the chain, itself, was solid gold with replacement parts, or a very good immitation of gold.

I figured there had to be a quick, on the spot test for the presence of gold.

Besides, I like to ask as non-specific questions as possible here, for they lead to best strings. Therefore the best opportunity for a beginner to learn from experienced persons, such as yourselves!

holt

Dr. Jon
06-03-2002, 03:32 PM
For chains the heft test is good onc you get the hang of it. Heft a gold chain and a filled one and you get the idea. Gold has density of about 19 versus brass which is about 7 and lead which is 11.

Hallmarks are not usually avaialble unless you encounter an English chain which will have a hallmark on every link.

Marks on the snaps are NOT reliable as they can be readily swapped about.

Hefting has helped me avoid many a trap. It is limited in that it takes a really good sense of touch to diostinguish 14 from 18K gold but I rely on it for solid versus gold filled.

Recall Archimedes did the same thing when he tested his King's crown. I have always wanted to try this so it is untested but here is what you can do.

Weigh the object in question. Drop it into a partially water filled measuring beaker the narrow tube kind calibrated in 1/10 cc's and compute the density.
Most gold allows are mixes of copper and silver. for 14 K with the rest silver the density would be about 16. If it were gold and copper its density would be about 15 grams per cc.

For 18 K the range is about 17 to 18 g /cc.

I have not done this myself but it si quick and won't damage the article.

The densities are approximate and also illustrate how with a bit of practice you can spot teh obvious fakes by feel.

There are a few metals with te same density as gold, platinum is a tad heavier but it is easy to spot and I'd let some one give me platinum for gold any day. Tantalum is also heavy and godl plated tantalum is potentially problematic but Tabtalum is hard to work and make into a chain so I doubt you will encounter it.

Tom McIntyre
06-04-2002, 03:03 PM
If you have a good balance, you can modify Jon's density test by weighing the item in air and submerged in water. The difference in weight can be converted to volume by using 1 gram/cc. The dry weight divided by the volume is the density.

This requires some kind of beam balance that you can place a container of water underneath.

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Tom McIntyre
Past President, NAWCC Chapters 174 and 87
Member Chapters 8, 87, 149, 159, 161 and 174
NAWCC: Crafts Committee, Web Committee
Pocket Horology Web (http://www.pocketwatch.org)
Tommy the JOAT's Web (http://www.AWCo.org)

Jeff Hess
06-07-2002, 06:00 AM
As promised here is the name of the new eletronic tester. This uses some "acids" that are pretty benign and is one of the "cleanest" that I have seen. It is a very small unit too. I purchased it at Florida Watch for I think 110 or 125. Good purchase... 727 327-1100 It is called teh MIZAR Tell them Jeff Hess sent you.