Precious Metal
Testing: Scratch Test Kits & Supplies
Scratch testing is one of the oldest
methods known to man for testing the karat of gold. In experienced hands, a scratch test is sensitive to within about +/-
½ karat or about 4%. In the hands of a novice, sensitivity is more likely to be about +/- 1-2 karat or 8%-16%. Kits come complete
with instructions
These kits are for testing gold, silver
and platinum. They come with gold test needles, wooden case, test acids and a scratch stone.
http://shorinternational.com/images/ImagesT/tes80800.gif
Precious Metal Test Kit with 3 needles
(10, 14, 18K) $55.00
Precious Metal Test Kit with 5 needles
(8, 10, 12, 14, 18K) $89.95
Gold Test Acid, 10 K; Gold Test Acid,
14 K; Gold Test Acid, 18 K each $4.95
Scratch Testing
for Gold, Platinum & Silver
CAUTION
Use extreme care in handling gold and
silver testing solutions, for they are, corrosive acids. In case of skin contact, flush with large amounts of water. Then
treat affected area with sodium bicarbonate or baking soda. If swallowed, contact a physician or hospital at once. In case
of spills. treat with water and then sodium bicarbonate or baking soda.
TESTING FOR
GOLD
1.
Scratch the piece to be tested over the surface of the black stone provided, press well using
4 firm strokes (two forward and two back) so as to leave a visible deposit, preferably a line of one to one-half inches long.
2.
Place a scratch line with a gold test needle next to the scratch line of the metal you are testing.
3.
Transfer a drop of the 10K solution to the
centre of the scratch made.
4.
Compare the speed at which the scratches dissolve to the needle scratch.
a. If faster, it is a lower karat than the10K gold
needle.
b. If the, solution leaves the scratch intact, it means
the object being tested is 10K or greater than 10K.
5.
The scratching and testing is repeated with the 14K solution.
a. If the Solution dissolves the scratch on the
stone, it means the object is less than 14K gold (if the scratch dissolves slowly and leaves rusty color particles, it is
probably 12k gold).
b. If the solution leaves the scratch intact, it means
the object being tested is 14K or greater than 14K.
c. Note: Many objects are marked 14K, but were fabricated
prior to 1982 when it was legal to mark items 14K, but in reality the gold was 13.5K. When testing 13.5K gold, the 14K solution
will not dissolve the scratch, but it will make it lose its brightness and it will turn it into a yellow-rusty color.
6.
The scratching and testing is repeated with the 18K
solution and the 22K solution (if available) until the karat of the object is determined.
7.
Remember that when the solution being used dissolves the scratch slowly and leaves rusty color
particles it is probably two karats lower than the solution being used.
8.
On items of heavy weight and volume such as chains, coins, etc, where plating could hide the true
metal, it is recommended that a deep notch in the test piece be made and the testing be made with the metal inside the piece.
9.
Apply a drop of Nitric Acid (for testing12 karat or under) to the scratch or notch.
a. If the object turns a bright green it is gold
plated or gold filled on base metal.
b. If the object turns a pinkish cream color it is plated
or gold filled on silver.
c. 10 karat gold will turn dark brown.
d. 12 karat gold will turn light brown.
e. 14 karat or higher will have little or no reaction.
TESTING FOR
SILVER
1. Scratch
the piece to be tested over the surface of the black stone provided, press well so as to leave a LARGE AND THICK visible deposit,
preferably a line of one to one-half inches long.
2. Transfer
a drop of the silver solution to the scratch made.
3. It
is possible to test directly on the piece being tested, however, the solution will dull the polishing of the piece, and leave
a mark where the acid was placed.
4. The
color reaction of the solution with the metal scratch will be as follows: (Take into consideration that the background of
the test stone is black).
f. 90%-100%= Creamy color
g. 77%-90% = Gray color
h. 65%-75% = Light Green color
i. If it turns darker green, it is plated.
TESTING FOR
PLATINUM AND WHITE GOLD
1.
Scratch the piece to be tested over the surface of the black stone provided, press well so as
to leave a LARGE AND THICK visible deposit, preferably a line of one to one-half inches long.
2.
Transfer a drop of the platinum test solution to the scratch made. (Take into consideration that
the background of the test stone is black).
3.
If the material on the stone is platinum, it should keep its white, bright color.
4.
When using Aqua-Regia, A platinum mark will remain
the same white color with no reaction.
5.
Platinum test liquid can also be used for 18k and 14K white gold.
6.
In the case of 18K, the material on the stone should start changing to a light bronze color in
about 3 minutes.
7.
For 14K white gold, the material on the stone should disappear in about 15 seconds.
8.
When using Aqua-Regia, white and green gold react slowly, but will still leave a brown mark after
applying acid.
Testing Palladium
1.
Rub the article on the test stone and apply a drop of Aqua-Regia.
2.
If it is genuine, the scratch will turn red.
Testing Gold and
Silver from base Using Schwerter Salts:
1. Testing
Silver, Gold Below 14 Karat and Base Metals with Schwerter Salts.
2. File a deep notch in the test piece and apply a drop of Schwerter's Solution in the
notch.
3. The
color reaction of the solution with the metal will be as follows:
Brass - Dark Brown
Copper - Brown
Nickel - Blue
Palladium - None
Gold - None
Silver Pure - Bright Red
Silver .925 - Dark Red
Silver .800 - Brown
Silver
.500 - Green
Lead - Yellow
Tin - Yellow
Testing Possible
Plated Gold Objects or Jewelry:
- Find a place on the piece of the object or jewelry where you can file a small groove without ruining the object or jewelry
- the intent is to penetrate the thin surface layer of plated metal (if it is plated).
- Try testing behind a link of a chain if you can - beware that it is not uncommon to use karat gold for clasps on chains
that are only plated with gold.
- Apply a drop of pre-mixed test acid in the small groove that you filed and note the color change if any (as above when
testing on a stone).
- Most jewelry pieces have areas of wear that can be good places to test. Occasionally the wear is sufficient to remove
any plating and testing these areas without filing can confirm that the jewelry is a lower karat than the test acid. If you
do try this and there is no color change, file a small groove and try again to be sure.
How to make Testing
Acid:
- Buy three small acid bottles with ground glass stoppers and applicators.
- Fill one bottle with "Liquid Nitric Acid".
- Fill the second bottle with Aqua-Regia (3 parts Hydrochloric Acid and 1 part Nitric Acid). The shelf life of Aqua Regia
is about 3 weeks so make a fresh solution of every three weeks.
- Schwerter's Testing Fluid is made by:
- Dissolving Potassium Dichromate Salt in1/4 oz distilled water, mixedl in a glass container, adding crystals until the
crystals quit dissolving.
- Then carefully add 3/4 oz Nitric Acid and fill the small bottle of the kit.
- This is used for testing gold below 14 karat and detecting base metals.
Care of your Gold
Testing Equipment:
- Mark each side of the test stone and always use Nitric Acid on one
side and Aqua Regia on the other side.
- If you use Schwerter Salts then purchase a second test stone, mark it and use it only for Schwerter Salts.
- Next, Wash the test stone in clean water after each use and completely dry it. Residual acid from a previous test may
yield incorrect results.
- Gold testing needle tips are actually made of gold wire and should have a long life. Clean and dry these before and
after each test to prevent contamination or false positives for higher Karats.
Here is one place to buy kits:
http://shorinternational.com/TestGold.htm
Gold Purity Standards
(by Karat):
24 K = 99.9% fine Pure Gold
23.5K = 97.92% fine
23 K = 95.83%
fine
22.5K = 93.75% fine
22 K = 92.67% fine Some coin, (not that of the U.S.).
21.6K = 90.00% fine The approximate
purity of U.S. coins
21.5K = 89.58% fine
21 K = 87.50% fine
20.5K = 85.42% fine
20 K = 83.33% fine
19.5K
= 81.25% fine
19 K = 79.17% fine
18.5K = 77.08% fine
18 K = 75.00% fine The highest grade of normally used in jewelry.
17.5K = 72.92% fine
17 K = 70.83% fine
16.5K = 68.75% fine
16
K = 66.67% fine This grade is commonly used in dental work ( 1/3 copper).
15.5K
= 64.58% fine
15 K = 62.50% fine
14.5K = 60.42% fine
14 K = 58.33% fine
13.5K = 56.25% fine
13 K = 54.17%
fine
12.5K = 52.08% fine
12 K = 50.00% fine Used in low priced jewelry (Half copper).
1.5K = 47.92% fine.
11
K = 45.83% fine
10.5K = 43.75% fine
10 K = 41.67% fine Used in low-grade jewelry such as class rings. Shows a marked
reaction to Nitric Acid.
9.5 K = 39.58% fine
9 K = 37.50% fine.
Silver Purity
Standards:
.9999 fine "Pure Silver"
.9584 fine "Britannia Silver"--Often used in manufacturing.
.9250
fine "Sterling Silver" Normally stamped "Sterling" or ".925"
.9000 fine "Coin Silver" antique items are marked "Dollar",
"D",".900", or "Coin Silver
"German Silver" is +/- 97% base metal and only +/- 3% silver, and thus has no bullion value
