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Touchstone does not sound like a strange word to us. From daily chats to the talks of the day, recognizing gold from imitations and touchstone, are familiar terms you may have heard about. The famous Iranian poet, Hafiz, introduces touchstones in one of his poems.
How great it would be if people are examined according to their experiences***This way anyone with impurities will stand out.
In this verse, the touchstone is introduced as a tool for recognizing real from unreal and pure from impure. Using touchstones in gold and jewelry industry is similar, since it helps recognizing pure gold from imitations. In this EG article, we will further discuss the touchstones and how they work.
The Importance of Genuine Gold
Gold authenticity has always been an important issue and people have always tried to find methods for recognizing gold from imitations. Gold has always been an important metal, that has been bought for investment purposes. Do you know how it is possible to distinguish gold from imitations? If you don’t, keep reading and we will say it.
Since this precious metal is very soft, it is usually on the market in the form alloys with different Karat levels and the more the amount of gold in the alloy, the purer the metal.
With regard to the fact that there are different portions of gold in different alloys, people prefer to buy purer metals which are of higher Karat levels. As a result, gold Karat has turned into an important issue.
To get more information about what gold karat is and how many grades it has, we suggest you studyour article titled as “How to distinguish Gold Karat“.
What Is Gold Touchstone?
The gold touchstone is a black stone made of Silica and quartz, that has no special shape and its main feature is its resistance against acid. In the far past, the stone was used to identify gold from imitations and secondly for evaluating gold karat.
This method is known as the most traditional method for recognizing gold purity and is used for pieces of small weight, but is not useful for gold bars. As a result, this method is not as frequently-used as it used to and other methods have replaced it.
Distinguishing Gold with Aqua Regia and Touchstones
Using Touchstones per se won’t help recognizing gold from imitations. In order to distinguish gold from imitations, and secondly to identify the gold karat, touchstones can help to some extent. You should pay attention that the touchstone temperature should be 37 centigrade degrees.
Next, you will need an acid which is called “aqua regia”. Aqua regia is the same as nitric acid, and is usually used to distinguish 17 or even lower Karats of gold.
By producing different concentrations of aqua regia and Hydrochloric acid, it will be possible to recognize pieces of higher Karat. Changing the aqua regia concentration makes it possible to identify different Karats of gold. This process is called grading. As a result, each type of aqua regia is capable of solving similar or lower Karats of gold,
Another point that should be taken into account is that since aqua regia is a kind of acid, it has corrosive properties. We use this acid together with touchstones since they are resistant to this acid and won’t face corrosion. When grading gold, silver, or platinum, grade only a portion of it and watch out for any contact between your hand or other parts of the metal.
Gold Karating Procedure
Before delving further into this, it should be mentioned that this method is only suitable for yellow gold, and karating yellow gold is done using the same method that has been employed for many years. Currently, however, LASER technology is used for karating white gold. For karating yellow gold, the piece must be drawn 20 times on the touchstone, until a trace of gold remains on the touchstone. Then pour a single drop of graded aqua regia on the lines you have drawn and weight for a reaction.
In this case, there are three possibilities. The first possibility is that nothing happens and no special reaction takes place. If so, the Karat level of both the lines you have drawn and aqua regia are the same, as a result of which no reactions have happened. You should also remember that if the Karat level of gold is higher than that of aqua regia, there will no reactions either.
The second possibility is that the lines you have drawn on the touchstone will go pale which means the acid has been capable of corroding the piece of gold and thus the piece has a lower Karat level compared to the gold Karat level.
The third possibility is that the lines will be wiped away completely which means either the metal is not gold or its an alloy with very little gold in it.
Aqua regia, however, has other capabilities as well.
Aqua Regia Application
With regard to the corrosive nature of the aqua regia, it is possible to use it without the touchstone too. To do you will need to use a sharp object to scratch gold slightly. Then pour a single drop of graded aqua regia on the piece and weight for a reaction. There will be three possible reactions.
The first possibility is that we will notice no reactions because both the aqua regia and gold have been of the same Karat level or the gold Karat level has been higher. But if gold turns black as a result of the reaction, it means that the Karat level of gold is lower than that of aqua regia. Finally if gold turns green, it means that the piece is not made of gold at all, or its an alloy with a very small portion of gold.
How To Clean Touchstones
After a while, there will be many lines on the touchstone, which were once drawn on the touchstone to assess gold karat. To use the touchstone again, you need to clean these lines in advance. In order to do this, you need to pour some aqua regia on the touchstone and scatter some salt on it. Wait shortly and then wash it.
Working with aqua regia is both easy and, of course, helpful. However, you might wonder where to buy aqua regia or the touchstone. The answer is quite clear: You can purchase these items from hardware stores that specialize in products for gold production and jewelry making.
Some Methods for Identifying Gold Karat
With regard to the fact that using a touchstone is an old method of recognizing Karat level, there are other ways which are both newer and more accurate than using touchstones. In the following, we will discuss some of these methods.
First Method: Assay Fire
Second Method: XRF
Third Method: Index Keys
Fourth Method: Ultrasonic
Each of these methods helps identify gold, and sometimes other precious metals Compared to recognizing gold with touchstones, these methods can confirm the purity of gold with more certainty. In the following, we will discuss each one briefly.
Identifying pure gold from impure or semi-pure pieces by XRF
In this method which is called the laser approach or the X-ray fluorescence, the piece of jewelry will be placed in the machine tank, and very soon all the components of the alloy will be identified.
Second Method: Assay Fire
The second method is among the aggressive methods, which is used to distinguish the gold in the mine soil. In this method, the samples will be placed in some special tanks called “Cupels” where they will be smashed, melted and finally by removing lead from it, pure gold will be achieved.
Index Keys
In this method there are some rods in the shape of keys, each of which is of a different karat. To identify the purity level of gold, we will need to draw two lines on the touchstone: one with the keys and the other with the piece of jewelry. Thus if both lines have the same color, they will be of the same Karat level.
Fourth Method: Ultrasonic
This is among the modifying methods in which high frequency waves with low amplitude will be sent into the piece. Each wave returns after coliding the existing breaks. One of the main advantages of this methods is correcting the defects in pieces of jewelry.
How to Recognize Pure Gold
So far, we have discussed some methods of checking gold Karat level. But if there is no access to the laboratory methods, there are simpler methods that can help you make sure about the authenticity of the piece.
Floating in Water
In this method, you will need to weigh the piece first, and then place it in a container filled with Distilled water, in a way that the piece goes completely under water. Now write the second number and divide by the first number. If the result was 19.32, it means that the piece is made of pure gold and unless, the gold has some impurities.
Carved Numbers
You might have seen numbers that are carved in the space of gold, silver and platinum pieces. These numbers and how they are written show the authenticity of the piece.
You may have already noticed number 750, in a rhombus.
In pieces of 925 Karat silver, we can see number 925 in a circle or an oval.
In pieces made of 900 Karat platinum, we can see number 925 in a cottage.
In a previous article titled “Methods for Distinguishing Gold“, the methods were discussed thoroughly.
Olympic Champions Methods
Olympic champions usually bite the gold medal when standing on the first stand. This is one of the methods of identifying gold Karat, and the softer it is, there will be a deeper trace of your teeth on it. The softer the medal, the higher the gold Karat level.
Conclusion
In this article, we discussed the “touchstone” as an old term in identifying gold from imitations. Touchstones, together with aqua regia work effectively in identifying gold from imitations and also determine gold Karat.
Today, however, there are more accurate methods that are approved of by experts in the field of gold and jewelry. Some of these methods are “XRF”, ”Assay Fire”, “index keys” and “Ultrasonic”. Besides these methods, we also mentioned domestic methods which help distinguishing gold from imitation.
If you plan to buy a piece of jewelry and want to be sure about its authenticity and Karat, we suggest you visit EG gold and jewelry store. You can get better ideas for making a purchase after reading our articles.
