Gold Testing with a Tri-Electronic Tester

Gold Testing with a Tri-Electronic Tester

Many pieces of antique gold jewellery (particularly from the Georgian era or pieces which are handcrafted) are unmarked and therefore gold testing is necessary. This article is a practical guide to using an electronic gold tester made by TRI electronics (I personally have the GXL-18 model.).  

This is my decimation of the information in the TRI Electronics user manual which I hope makes a good quick reference for those interested.  HOWEVER – PLEASE ALWAYS REFER TO THE MANUFACTURERS INSTRUCTIONS FOR THE FINAL SAY ON HOW TO USE THESE TESTERS. 

 

OPERATION PROCEDURE

The procedure for testing can be shortened to the following easy to remember four words:

LOAD – CONNECT- SELECT- TEST

For more details, see below: 

1) Load the polyethylene gel tube in accordance with the manufacturers instructions.

2) Connect the following:

a) The black wire to the sensor’s plug outlet.

b) The black and red wire connector to the display unit.

c) The red wire to the testing plate.

3) Turn the unit ON. The unit should now read ‘G-XL-18 READY TO TEST…’

4) Selecting a point to test: 

a) Make sure the point to test is close to BUT NEVER TOUCHING the alligator clip.

b) Do not allow the gel to touch the alligator clip as this will corrode it.

c) Thoroughly clean the testing point with the eraser.

5) The First Part of the Test

  1. Place a tissue, paper towel or rag under the tip of the sensor.
  2. Hold the sensor in a vertical position with the nozzle down.
  3. Twist the Rotary Cap counter clockwise, one click at a time, until a drop of gel appears.
  4. Wipe this first drop of gel away.
  5. Turn again (usually one or two clicks) until more gel appears.
  6. Touch the sensor to the selected area of the test object.

6) Select a gold colour button. 

Depending on the visible colour of the metal you are testing, select one of the following buttons on the unit (see manual for diagram of button locations):

Y-Yellow

W-White

R-Red

G-Green

7) Keep the sensor in a vertical position for about 5 seconds. This is is when the gold value is calibrated.

8) The karat value and European Standard are displayed on the instrument. (Tip: Write this down with a pen and paper you keep to hand, along with your reference for the item).

9) Turn off the instrument.

POINTS TO KEEP IN MIND

1) Electronic tests are not infallible.  If you achieve a result which is outside of expectations then retest in a different location after cleaning your equipment and your item and use new gel. Keep testing until you get a consistent result. Always make a note for the customer if you are selling gold items tested with an electronic tester explain that the test is not infallible and should be seen as a guide only. 

2) Be careful with fine chains. Very fine chains  can be crushed by the dispenser. Avoid pressure with fine gold chains whilst keeping gel contact. It’s recommended to get the results of two or three tests.

3) Be aware of air bubbles. Sometimes air bubbles with give a high or low reading. Always retest and apply common sense to the results of your readings.

4) Clean Tip. A clean tip is essential for an accurate reading.

a) If you are not using the gold tester more than once a week it is advised that you remove the gel tube from the sensor and store it to keep the gel from drying out.

b) Before replacing the gel, whether with a new tube or with one previously removed, clean thoroughly with SC-10 Cleaner Kit. 

c) If the tester has not been used for over a week, clean the tip with the plastic cleaner provided by inserting the tip into the nozzle of the sensor.

d) If gel drops are not dispensed by rotating the twist cap, clean the sensor with the SC-10 Cleaner Kit. 

5) Solder areas and heavy castings with unevenly dispersed metal can give false readings. Always retest in different areas of the piece.

6) Italian Gold may be waxed and can give a false reading. If you suspect the metal may be waxed, clean the testing area with heavy erasing or with nitric acid (only a drop is required).

7) Skin oils can give a false reading. In heavily worn pieces clean the testing area first with the eraser or with non-acetone nail polish remover.

8) Plated Gold. Usually a tiny scratch or a pin prick will allow gel penetration to the base material on plated pieces. If this is not sufficient, two or three tests are recommended with a thorough eraser cleaning in between. If the item is gold plated, the karatage will decrease with each testing. A solid gold piece will not decrease with each test.

9) Dispose of the drop of gel following each test. 

10) Use every other gel drop for best results. 

11) DO NOT LET GEL OR SENSOR NOZZLE TOUCH THE ALLIGATOR CLIP!

12) When removing the cable from the sensor, do not pull the wire! Pull the plug itself to avoid damage. 

13) Testing objects larger than the Alligator Clip. In this instance, unhook the red wire from the testing plate and proceed with the test as per instructions but with the tip of the red wire touching the object.

14) Do not retest the same spot without eraser cleaning.

15) Refer to the manual for full care and maintenance of the tester and follow their recommendations.  

TROUBLE SHOOTING

1) Problem: Brown spot on test surfaces

Solution: Rub the spot with eraser

2) Problem: Display unit reads “NOT GOLD”

Solution: Check the wire contacts and the connections

3) Problem: Display has no reading

Solution: Check batteries or switch to converter or change the wire set.

4) Problem: Inaccurate or different readings

Solution: Keep gel away from alligator clip

5) Problem: Gel does not come out

Solution: Clean sensor nozzle and check gel tube and replace if empty.

6) Problem: Sensor’s rotary cap is hard to turn or is tight.

Solution: Check gel tube and replace if empty.

7) Problem: Changed or reduced karat value on the display from previously.

Solution: Check gel tube and replace if empty.

Copyright © 2017 by Pippa Gaubert Bear and Elder & Bloom. Unauthorized use and/or duplication of this material without express and written permission from this website’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Pippa Bear and Elder & Bloom with appropriate and specific direction to the original content.

Welsh Gold

a painting of two women in traditional dress against a mountainous landscape
William Dyce, Welsh Landscape with Two Women Knitting (1860)

Welsh Gold is considered to be among the world’s most sought after and valued gold because of its scarcity and beauty.  It comes from two areas of Wales, one in North Wales, in the areas of Barmouth, Dolgellau and Snowdonia and the other area is in South Wales, in the valley of River Cothi at Dolaucothi. At present, there are only three companies licensed to work with pure unmixed Welsh Gold (one is listed in the links at the bottom of this page).

It currently sells for approximately $1500 ounce.  There are no active gold mines currently in Wales, so all Welsh gold comes from a diminishing supply.  It is illegal to prospect for gold in Wales.

Misconceptions.

There are a number of misconceptions about Welsh Gold.  One is that it is naturally Rose Gold in color.  This is simply due to copper and gold having often been a popular alloy throughout the ages, especially in Britain.  In its natural state, Welsh Gold is either the usual yellow gold color or it can be somewhat whitish as it can be found alloyed with silver in its natural state (this is called electrum). However, I have also read that Welsh Gold used to be naturally alloyed with copper and it is only in recent years that it is always purified so I am not certain of the truth.  Regardless, Welsh Gold is not actually much different in chemical composition from gold from anywhere in the world.  It is perhaps simply the psychological appeal of having gold from Wales that gives it its value.

The other very widely spread misconception is that jewelry commonly sold as ‘Welsh gold’ contains more than a tiny percentage of Welsh gold.  Often it is literally just a touch of Welsh gold and the rest is gold bullion.  Watch out for the words ‘presence of Welsh gold’ and ‘contains Welsh gold’.  A genuinely pure Welsh gold item is very valuable and rare.  In contemporary jewelry, a piece with 10% Welsh gold is about the highest percentage available.

Assay Marks

When only gold of Welsh origin is in the piece, it will have this assay mark (Aur Cymru):

The Aur Cymru stamp is three feathers:

As with other British gold pieces, you will also see:  The Goldsmith Makers Mark, The Assay Standard Hallmark, The Assay Office Mark and The Date Letter.

The Welsh Dragon Mark on a piece means that Welsh Gold is ‘present’ but it doesn’t say by what percentage.

hm-dragon

Other unique marks you will see will be makers marks of Welsh jeweler’s but they do not mean that the gold is purely Welsh gold, only the AC mark will mean that.

Royal Connections.

Since 1923, Welsh Gold has been favored by the British royal family which has consequently enhanced the value of Welsh gold even further.

Kate Middleton wearing her engagement ring

Kate Middleton wearing her Welsh Gold engagement ring.

Sources / further reading:

http://www.clogaugoldmine.co.uk/#

http://en.wikipedia.org/wiki/Welsh_gold

http://www.welshgoldplc.co.uk/pages/assayinfo/index.html

http://www.kelvinjenkins.co.uk/WelshGold.shtml

http://www.bbc.co.uk/news/uk-wales-south-west-wales-13196514

http://www.ecouterre.com/kate-middletons-royal-wedding-ring-is-made-from-repurposed-local-welsh-gold/

http://www.wartski.com/

http://americas.visitwales.com/news-and-features/hiraeth-for-beginners/welsh-gold/

http://www.rhiannon.co.uk/

http://www.rhiannon.co.uk/faq

Electroplating, Rolled Gold, Gold Fill, Goldtone and Vermeil

A GROUP OF ENGLISH AND CONTINENTAL GOLD, GOLD-PLATED AND SILVER ARTICLES,

A GROUP OF ENGLISH AND CONTINENTAL GOLD, GOLD-PLATED AND SILVER ARTICLES
Christie’s 2536

Plated Metals

Any jewelry that has an overlay of another metal, no matter the means of production, is called plated jewelry.  Electroplating is when a base metal is coated in a thin coating of another metal, usually gold or silver, by putting the base metal in a chemical solution and using an electrical current to deposit the layer of other metal.  Electroplating was first patented for commercial use in 1840 in Birmingham.  The process soon spread around the world.  The first modern commercial electroplating center was opened in 1876 in Hamburg.

Jewelry marked H.G.E. or H. G.P. has been gold plated or ‘hard gold electroplated’. 

Vermeil is the highest quality kind of goldplated metal, and is made with a sterling silver base coated with gold. Goldtone jewelry is when the jewelry is coated in a gold colored metal that isn’t gold at all; this is common with costume jewelery such as Monet, Napier, Robert and Kramer.

One way to identify gold plated or electroplated jewelry is to look at the corners and edges with a loupe.  If there are any worn areas with a different type of metal showing through this means it is plated metal. Another way to test is with an electronic gold tester.  Acid test kits can’t differentiate good gold plated jewelry from gold jewelry as the acid only tests the surface of the metal.

Gold Fill or Rolled Gold

Brooch

Brooch, stamped rolled gold (copper alloy) with pearl
V&A Museum

Gold Fill is the same as Rolled Gold or Rolled Gold Plate (the first is the American name and the later two are the British names).  It is usually more valuable than gold plated metal as it generally contains more gold.  Gold-filled  or rolled gold jewelry, is composed of a solid layer of gold bonded to a base metal such as brass. This bonding is created with a process using heat and pressure.

In the USA, if the gold layer is 10 kt fineness the minimum layer of karat gold in an item stamped GF must equal at least 1/10 the weight of the total item. If the gold layer is 12 kt or higher the minimum layer of karat gold in an item stamped GF must equal at least 1/20 the weight of the total item. Gold Fill can be identified by fractional numbers and letters surrounding the karat quality mark. Gold Fill is expressed in a fraction: 1/20 10K G.F., for example, translates as: 10 karat gold comprises 1/20 of the weight of this object. Gold-filled is expressed as: GF, gold filled or, in French, double d’or.  RGP means ‘rolled gold plate’.

Double clad gold-filled sheet is produced with 1/2 the thickness of gold on each side. 1/20 14Kt double clad gold-filled has a layer on each side of 1/40th 14Kt making the total content of gold 1/20.

Some antique jewelry is made with gold fill with a base of silver and this is considered the highest quality gold fill.  Gold Fill was first used in the USA in 1844.

Gold Fill will loose heat faster than solid gold. It may or may not be magnetic, depending on the amount of gold and what base metal has been used.  It can be tested with acid testing or an electronic gold tester.

Sources / further reading:

http://www.langantiques.com/university/index.php/Electroplate

http://en.wikipedia.org/wiki/Electroplating

http://wiki.answers.com/Q/What_does_the_term_%27electroplated%27_mean_regarding_jewelry

http://www.ehow.com/how_5841642_identify-gold-plated-jewelry.html

http://www.ehow.com/how_5172348_verify-gold-plate-gold-filled.html

https://pippatreevintage.wordpress.com/2013/03/08/evaluating-a-rolled-gold-phoenix-locket/

http://en.wikipedia.org/wiki/Gold-filled_jewelry

http://www.artisanplating.com/articles/goldfilled.html

Chains

Antique Ladies Watch

Late Victorian lady with gold chain and watch.

Metal jewelry chains  are something we take very much for granted.  Since the chain making process became industrialized in the mid to late 1800s, we have come to expect plentiful, inexpensive and uniform chains for all our jewelry.  However, it is important to remember that chains were once made entirely by hand, usually by soldering one link at a time.  The genuinely handmade chains, whether gold, silver, copper or an alloy, are really very special and rare indeed and would have been treasured and highly valued by their original owners. Generally speaking, a handmade chain will be made with much longer and larger links than a machine made chain as it really is labor intensive to make a chain by hand.  There was also a long interim period in history when the links were machine made or stamped but the chains were hand-assembled. I will do my best to get more precise details on this soon.

Victorian lady wearing pearls and a slide chain. Slide chains were very popular in the late Victorian era.

Chains have been loved in all eras, but in the mid-Victorian years their popularity reached a peak.  In 1864, Peterson’s Magazine noted, ‘Necklaces are almost indispensable now with low dresses. Bold chains are six and eight times doubled and fastened here and there with thick round balls of gold, inlaid with jewels; the same style with pendant ornaments, is pretty for bracelets.’

The most common ways that chains were worn by women in the Victorian era were: slide chains, chains with a locket on and also a very long chain.  Men of course wore watch chains.

Victorian lady wearing a locket on a chain.

Portrait of an Early Victorian Woman

Portrait of an Early Victorian Woman wearing very long gold chain.

Gustav Klimt (1862-1918): Portrait of Marie Breunig

Gustav Klimt (1862-1918): Portrait of Marie Breunig
This Art Nouveau era lady appears to be wearing a fine gold chain collar with pendant.

In the Art Deco era or course very long chains were extremely popular.  Here is a contemporary actress dressed in Art Deco era costume.

lady edith2

Lady Edith wearing very long delicate chain.

Necklace

Heavy gold chain, c.1860, England
V&A

Necklace

Shell cameo necklace, connected with gold chain.
c. 1800, Italy
V&A Museum

 

Here is an overview of all the kinds of chains that are commonly used in jewelry (I will be returning to this post to update as I find out more about each kind and hopefully find pictures for all of them over time):

Albert or Vest Chain

Albert Chains were named after the style of watch chain Prince Albert wore.  They were popular in the Victorian era. They have a bar on one end which is used to attach it to the vest button hole. The opposite end of the chain has a swivel hook to attach the watch. The chain is left exposed and often has a decorative fob. The watch is then worn in the vest pocket. ‘Victoria’ Chains were like Albert chains but were for women.

Alma Chain

An alma chain has a ribbed surface and broad links.

Anchor Chain

These are named after the chains used for ship’s anchors.  They are the same as a cable chain but with an extra cross bar.

Bead

A bead chain has small balls of metal joined by small lengths of wire, not longer than each bead in between.

Belcher or Cable Chain

A belcher or cable chain is the most classic kind of chain, made with interlocking links.

Benoiton

A benoiton is worn in the hair and consists of several chains which dangle from the hair and are then attached to the bodice.  This was a brief fashion after the success of the comedy “La Famille Benoiton” by Victorien Sardouin in 1866.

Book or Venetian Chain

A book or venetian chain resembles a book binding having interlocking, folded links of flat metal.  It was popular in the Victorian era.

Briolette or Box Chain

A briolette or box is similar to a belcher chain except the links are tighter together and are square in shape.

Byzantine Chain

An intricate and complex chain that needs to be seen rather than described.

Curb or Gourmette Chain

A curb chain is made from round or oval interlocked links which are twisted until they lie flat. They can range from slightly flattened to completely flat.  They can be solid or hollow and can be interlocked with other styles of china.

Figaro Chain

This is the same as a curb chain (see above) but the links have alternating lengths.

Herringbone Chain

A herringbone chain is formed with V-shapes and will lay entirely flat.

Prince Of Wales

A Prince of Wales is a twisting chain made of circular links.  Each single link has at least four others joining into it.

Rope

A rope chain creates has two twisting spiraled strands, created by many unjoined links.

Singapore

A Singapore chain can also be called a twisted curb. The links are joined in such a way that, even when the chain is untwisted, there is a curve to it.

Snake or Brazilian Chain

A snake or Brazilian chain is an articulated chain, designed to move like a snake.  It was first introduced in 1850.

Spiga

A spiga chain has figure-eight links that form a 3D chain.  It seems  almost square, and looks as though the wire has been braided.

Trace Chain

A trace chain is usually the simplest type of chain.  The links are usually uniform in breadth and thickness.

Waldemar Chain

This is another kind of pocket watch chain, similar to an Albert chain.  It has a swivel catch on one end to hold the watch and a spring catch on the other for an accessory.  They were worn across the vest from the left pocket to the right.

Wheat Chain

A wheat chain is made of  long, thin teardrop-shape links that all point in the same direction. The join of each link is like a tiny hinge.

Sources / further reading:

http://www.langantiques.com/university/index.php/Chain

http://en.wikipedia.org/wiki/Jewelry_chain

http://www.antiqueweb.com/articles/antiquecostumevintagejewelry2.html

http://www.morninggloryantiques.com/JewelChatVictLkts.html

http://books.google.de/books?id=WVUSj7-ldtMC&pg=PA33&lpg=PA33&dq=benoiton+chains&source=bl&ots=XsrNeAVccT&sig=qU9kOiMhW5oPWecz26kZ9NBvI9I&hl=en&sa=X&ei=RLESUYS-EYLJ4ASN5ICACQ&ved=0CEIQ6AEwAg#v=onepage&q=benoiton%20chains&f=false

http://www.antiquetrader.com/features/jewels_of_southern_belles_northern_beauties

Understanding gold

The use of gold in jewelry in every era is so completely ubiquitous that it is easy to forget that gold itself is also subject to the ebb and flow of fashion.  Each era, with it’s particular technical abilities, sensibilities and levels of wealth has a different relationship with gold in jewelry.  Gold, the most malleable of all metals, can be utilized by the jeweler in a variety of ways: chasing, repoussé, filigree, cannetille, soldering, granulation, piercing and casting.  Indeed, gold’s relative level of scarcity in any given era has been the driving force between many creative breakthroughs in jewelry design.  Many of the aforementioned techniques are designed to increase the appearance of volume in gold and to maximize its impact.

There is really a great deal to say about gold so I would like to focus as much as possible on the basic and practical aspects of understanding and evaluating gold in an antique jewelry piece.

A diamond-set locket

A Diamond-set gold locket
Sale 8127
Jewellery
16 January 2013
London, South Kensington

Understanding gold basics

Karat

Up until the mid 20th century, gold has always been measured in karats (also written kt or k). This is not to be confused with ‘carat’ which measures gem weight. However, in Britain and some other countries ‘karat’ is spelled ‘carat’ just like gem weight.  (Confusing I know!)

The ‘fineness’ of gold refers to the amount of actual gold present.

One karat is 1/24 of the total purity of the gold.

Therefore:

24 k gold is 99.99% pure gold.

18 k gold is 75 % gold and 25 % another metal

14 k gold is 58.3% gold and the rest is another metal

10 k gold is 41. 7% gold and the rest is another metal

etc

Another, possibly easier way, to say this would be to say:

24 k is 24 parts gold

18 k gold is 18 parts gold, 6 parts another metal

14k gold is 14 parts gold, 10 parts another metal

10 k gold is 10 parts gold, 14 parts another metal

etc

Non-karat gold

In the USA the following applies: lower than 10 k gold is not allowed to be called ‘karat gold’

In the UK the following applies: lower than 9k is not allowed to be called  ‘karat gold’

In Germany the following applies: lower than 8k gold is not allowed to be called ‘karat gold’

Below these amounts, gold is not considered to be karat gold and is normally referred to as ‘low-karat gold’ or ‘a gold alloy’ or ‘coin gold’.

Gold colors

There is only one color that actual 24k gold can be.

In order to make it all the different colors, gold is alloyed with different metals in different quantities to achieve the variety of results we are familiar with.

Normally, gold is referred to as being one of the following:

Yellow gold – this is when it is alloyed with gold, copper, silver and zinc

Bracelet

Gold ‘Manchette’ or cuff bracelet, c. 1860, England
V&A Museum

Rose gold – this is when it is alloyed with copper and silver, with proportionally more copper than silver.

Antique Rose Gold Bracelet.

Rose Gold Bracelet, c.1900

White gold – this is when it is alloyed with nickel or palladium, copper and zinc

BRACELET ART DECO DIAMANTS

Art Deco diamond, white gold and platinum bracelet
Sale 3517
Paris Jewels
5 December 2012
Paris

Green gold – this is when it is alloyed with gold, copper and silver, with proportionally more silver

Rose and green gold woven bracelet.

Hallmarks

Purity marks

Gold has been purity marked  since the Middle Ages and this is a very useful way of understanding the karat of gold, as well as helping to give an indicator of age and origin. The purity mark is one of the very first things to look for when evaluating a piece of jewelry.  A purity mark indicates the percentage of precious metal in the piece.

Generally, countries which have used non-metric systems such as the USA and Great Britain, will have a purity mark for gold written as follows:

24 k, 18 k, 14 k, 10 k, 9 k, 8 k (or in the case of the UK – 24 ct, 18 ct etc)

Countries which have traditionally used the metric systems, such as continental European countries, will have purity marks for gold written in the following way:

1000/1000 is pure gold and will be marked as ‘1000’, 750/1000 is 18k gold and will be marked as ‘750’, 583/1000 is 14 k gold and will be marked as ‘583’, 333/1000 is 8kt gold and will be marked as ‘333’

In addition, many countries use a pictorial mark to indicate purity so it is best to refer to a library (see resources at the bottom).

Responsibility marks

The  ‘responsibility mark’ is also known as the ‘maker’s mark’ as well as the ‘manufacturer’s mark’. This doesn’t necessarily name the maker but rather who is responsible for the stated purity of the metal. In countries with a long  tradition of mandatory maker’s marks, these marks were always unique to each maker.  They usually had the initials of the maker with a pictorial image. Sometimes, the maker’s marks had to be a specific shape, for example the lozenge shape in France which became mandatory from 1797 onwards. In the USA these marks were made mandatory in 1961. On English, and later on USA, pieces you frequently see an ampersand (for example S&P). Maker’s marks were normally struck by the manufacturer and registered at the assay office.

Dateletters

In the UK, Dateletters have been used since 1478 and gold and silver had to be marked at the “hall’ (hence the word “hallmark). A new letter of the alphabet was used every 25 years (some letters were skipped). A different letter font and/or design of the letter border was used every cycle to differentiate.  This gives jewelry historians an excellent way to find the age of a piece.  Very delicate pieces, however, did not have dateletters as there was no room to put them

Other Marks

Town Marks

Specific towns took on their own marks.  For example, a famous one is Birmingham’s anchor.

Tally marks

Sometimes found on UK and USA items.

Duty marks / Import and export marks

Indicated taxes paid or if exempt

Retailer marks

Usually just large stores, ie Tiffany’s

Patent and inventory marks

Usually long numbers, useful in dating. Firms like Cartier use.

Designer marks

Used quite frequently from the Art Nouveau era onwards

Gold purity according to era and country

24 k gold is very soft and generally considered too easily damaged to create jewelry from. In past eras, the people who could afford gold did not do household chores so their jewelry didn’t need to be hard wearing.   As gold came to be worn more and more by regular people, alloys were created for jewelry wear to give strength and durability. Generally speaking, gold from the Georgian era is much more likely to be higher karat than later eras. The Victorians began to cater to the tastes of people who weren’t royalty by creating more practical gold alloys.

As you can see below, gold purity marks can give us a lot of information regarding possible age of the jewelry and also country of origin.

UK and Ireland

Up to 1854, the legal standards for gold were 18ct and 22 ct.  In 1854, 15ct, 12ct and 9 ct were introduced.  In 1932, the 14ct mark was introduced, and the 12ct and 15 ct marks were eliminated.

USA

Prior to the year 1906, most jewelry made in the USA was without any kind of mark.  After this, gold purity marks can be identified as being American by the use of ‘k’ (as opposed to ‘ct’ from the UK).

Germany

Before 1884, German gold purity marks was expressed in “Löthig”.  Pure gold was 16 löthig.  So, for example, if you see a piece with ’13’ marked on it, it might well be expressing 13 löthig, which would indicate 812.5/1000.

From 1884 to the current day, German gold purity marks could be expressed in thousands (such as 585 for 14 karat gold) or expressed as a karat like the USA (for example 14k).  They could also have both marks on one piece.

France

From1838 an eagle’s head has been used to indicate a gold purity of at least 18 karat.

In France, gold jewelry must have at least 18 karat unless it is for export.  Items for export have pictorial marks representing 9 k or 14 k.

Weight of gold as a indication of value

The value of a piece of jewelry is not only indicated by the purity of the gold, but also by the weight of that gold.  It is best to weigh jewelry with a specifically designed sensitive gram scale. In order to calculate the value of the gold itself, if you were simply to look at scrap value, there are various sites online where you can find out the daily price by putting in the weight and the karat of the gold.

Testing gold

Sometimes, it will be necessary to test a piece of jewelry for gold content.  This can be because the hallmark was worn away, because there is no hallmark or because you don’t entirely trust the hallmark.

Gold is not magnetic, so a quick way to eliminate non-gold is to test with a magnet.

There are several different ways of testing gold and metals.  One of these is the acid scratch test.  I will write a separate post at a later date all about testing metals as there is quite a lot to it.

Gold substitutes and look a likes

These include, but are not limited to: pinchbeck, ‘tombak’, ‘schaumgold’, brass, bronze, copper alloy, gold fill, gold plate, painting gold etc etc (I will go into all of these in more detail in the future).

Sources / further reading (be sure to have a look at the sources in the drop down menu also):

http://en.wikipedia.org/wiki/Carat_%28purity%29

http://www.langantiques.com/university/index.php/Gold

http://www.silverresearch.org/

http://www.langantiques.com/university/index.php/Hallmarks

http://www.nma.org/pdf/gold/gold_history.pdf

http://www.nma.org/pdf/gold/gold_history.pdf

http://www.ehow.com/how_2095334_make-fools-gold.html

http://www.925-1000.com/

http://www.langantiques.com/university/index.php/Category:Maker%27s_Marks