Wednesday, November 28, 2012

Exploring the Technical Process of Minting Precious Metal Coins in China and Early Sand Blasted (Matte) Coins

By Huang Ruiyong

Translator's note: "sand blast" refers to the process to produce effects normally known as "frosting" and "matte" on coins. Since the term "sand blasting" is used in Chinese to cover both, I am doing a direct translation to be consistent. English readers should be able to figure out when it refers to frosting and when to matte. Also, I added some pictures to the original post to show some of the coins.

Silver coins are small and delicate,

Requiring highly sophisticated minting process,

Mirror fields and frosting are both gorgeous,

Sand blasting is especially important.

Year of Children takes the center,

Followed closely by Soccer and Volleyball,

Alpine Skiing is most lovely,

All glitter on the dome of sky.

A poem to the tune of Qingpingyue

Good evening, everyone. The topic tonight is the technical process, and sand blasted coins of the early years from the PRC will also be discussed in the meantime.

This is a very important topic. For coin collectors, understanding the technical process is like learning how to swim. With such understanding, they can feel at home in the ocean of precious metal coins.

First let's discuss the technical process.

We all come across two simple terms from time to time: proof coins and BU coins. Probably every coin collector can give some features of these two types of coins, but what are their accurate definitions?

In general, "BU" comes from "Brilliant Uncirculated" in English, meaning uncirculated coins with mint luster. On the other hand, "proof" in English means "minted with great care."

Now we run into a problem, because in our country, collectors normally distinguish BU coins and proof coins based on the mirror field. Coins with mirror fields are considered proof coins, and coins without mirror fields are normally treated as BU coins.

However, internationally many coin catalogs and numismatists hold a different view than the criterion above. In reality, we cannot use the mirror field as the only criterion for proof coins against BU coins.

Let's look at BU coins first, and return to proof coins later.

BU coins fall into the following categories:

1. BU coins with mint luster, "BU" in its true sense. These are coins struck under pressure, with mint luster, such as the Fat Man, and Sun Yat Sen coins;

2. Coins treated with sulfuration, with the color of ancient silver, which results from the reaction of silver to potassium sulfide solution. These coins can be played with in hands, such as the Beijing International Coin Expo coin;

3. Common BU coins, such as BU silver pandas in several years, Auspicious Matters, and some Guanyin coins. These coins do not have mirror fields in the strict sense, with a dull surface that cannot reflect human images.

Are sand blasted coins included in BU coins? It is premature to reach a conclusion now. Let's see how sand blasted coins are minted.

Many coin collector friends are mistaken in their understanding of the technical process for minting sand blasted coins. This is the process in their understanding: Working dies, usually made of steel, are needed to mint milled coins. But many people may think that striking machines apply pressure on the die, to produce coins with mirror fields from silver planchets, and then fine sands are blasted through a high pressure gun on the coins, to form sand blasted coins.

But this understanding is wrong. If the minting process followed these steps, we would see that:

1. Silver coin production is highly costly;

2. The surface of the silver coins will look very unsightly, like a human face ravaged by small pox, with little pits and hollows everywhere.

What is the correct technical process to mint sand blasted coins? There are two approaches.

1. Blast fine sands evenly to the working die, and then strike to produce sand blasted silver coins;

2. Mint mirror coins with a mirrored working die, and when the production quota is met, blast sands on the working die, to strike sand blasted silver coin in the same fashion.

People may ask: why there are different effects among sand blasted coins? They have this question because some of the sand blasted surfaces are dark, which we call "dark sand blast", and other sand blasted surfaces are bright, which we call "bright sand blast." Examples of each include the kilo silver Horse, 8 gram and 15 gram lunars, and dodecagonal coins.

The answers are:

1. Sands used are different. Slightly different sands can lead to various appearances in color and luster;

 2. How long the working die has been used. Freshly sand-blasted working dies leave a striking effect on silver coins. With more coins struck, the sand-blasted effect will diminish gradually.

Now that we know how sand blasting works, let's come back to the discussion of proof and BU coins.

Proof coins require meticulous workmanship. It is true that a high quality mirror field is a sign of such meticulous workmanship, but I tend to believe that some coins can qualify as proof coins based on their finely sand-blasted surface. For example, the 2oz Longmen Grotto silver coin does not have any mirror field. Only sand blasting and anti-sand blasting technologies were used on it. For this reason, we can define this type of coins as proof sand blasted coin.

(Longmen Grotto)

The same goes for the colored Red Cross silver coin and the 2oz Maijishan silver coin. They both have one mirrored side, and the other side is sand blasted. But they are definitely proof silver coins.

So at this moment, we should all be clear about the definitions of proof coins and BU coins. Please note that the mirror field cannot be used as the sole criterion to distinguish the two, just as market economy is not the only criterion between socialism and capitalism.

Now that we have the sand blasting technology, its twin brother anti-sand blasting technology would be naturally invented in time. What is anti-sand blasting, then?

Everyone knows that sand blasting was invented for the relief part on precious metal coins. The bottom of the coin is a mirror field, and the relief is sand blasted. This brings out the best contrast on the coin.

But how about sand blasting the field of the coin, while leaving the relief part bright and shiny? It has been proved that if the technologies are aptly applied, this kind of coin is also eye catching. This process is what is normally known as "anti-sand blasting."

The anti-sand blasting technology was first applied on the 1992 panda gold and silver coins. Before that year, the Temple of Heaven occurred on the obverse of all panda coins, in the form of a sand blasted image. Starting in 1992, onto 93, 94, 95… the Temple of Heaven changed to the anti-sand blasted form, to the great joy of panda fans.

(1993 silver Panda)

Talking about the anti-sand blasting technology on panda coins, we are obliged to highlight the painstaking efforts by metal coin designers of our country. We all know that the 83 gold Panda designed by Mr. Chen Jian won the honor of Best Gold Coin international award, which laid a solid foundation for Chinese precious metal coins to be recognized internationally. Mr. Chen Jian made use of raised and sunken surfaces in the engraved image to mimic the black and white color of pandas. But after that, due to the continuous releases of panda coins and medals, all panda movements were presented on the coin, in an effort to avoid repetitions: pandas playing, drinking, having fun with water, mother and cub, strolling, eating bamboo… What was missing might just be pandas relieving their bowels. What was the way out?

Fortunately, the anti-sand blasting technology came to the timely rescue in 1995. After that, panda's black and white colors are presented in greatly enriched ways. Starting from 1995 till now, the anti-sand blasting technology has been used to show the cuddly pandas.

(1995 Panda)

Apart from the panda coins, anti-sand blasting was applied to other themes as well: the river next to the girl on the 1992 Environmental Protection silver coin, the 1997 Peacock coin, and the flyover on the 2002 Beijing Coin Expo coin. But the most applaudable application of the sand blasting and anti-sand blasting technologies was the 100th Anniversary of the Dunhuang Caves Discovery silver coin set. The Sixteen Country Flying Apsaras, the Beiwei Flying Apsaras, the Xiwei Flying Apsaras, the Beizhou Flying Apsaras, the Sui Dynasty Flying Apsaras and the Tang Dynasty Flying Apsaras float through the sky gracefully, or appear with a dignified bearing, or rise with the wind. All this, in addition to the most exquisite packaging, is intoxicating beyond description.

(1992 Environmental Protection)

(1997 Peacock)

(flyover on the 2002 Beijing Coin Expo coin)

(Sixteen Country Flying Apsaras)

Sand blasted silver coins that leave the deepest impressions on me include the following gems (many of which are award winners):

1986 27 gram Sun Yat-Sen: this is a coin with coin alignment. The sand blasting effect of Sun Yat-Sen's head portrait exceeds that on most coins released in the 20 years since then.

(1986 27 gram Sun Yat-Sen)

1990 Woman Diving: the elegant figure makes a beautiful curve in the air. It was absolutely qualified for the Ten Best in the world for that year.

(1990 Woman Diving)

1993 5oz and 20oz silver Peacock: every feather is strikingly carved in great detail. The master piece from Giuseppe Castiglione well deserves its fame.

(1993 5oz Peacock)

2001 Dunhuang Tang Dynasty Buddha: the holy appearance is both stately and life-like. One can never over-praise the World's Best Coin that combines high relief, sand blasting, anti-sand blasting, a beautiful mirror field and piefort technologies in one.

(2001 Dunhuang Tang Dynasty Buddha)

Next we will focus on the four top gems among the early sand blasted coins from China.

The accurate term for the early sand blasted coins from the PRC, such as Year of Children, Women's Volleyball, Men's Soccer, China Empress, Men's Alpine Skiing and the 1989 Save the Children Fund (whether it should be categorized as sand blasted or light BU is still under discussion), should be: fully sand blasted BU coin.

(Year of Children)

(Women's Volleyball)

(Men's Soccer)

(China Empress)

(Save the Children Fund)

Among them, Year of Children, Women's Volleyball, Men's Soccer and Men's Alpine Skiing are the four top gems among early fully sand blasted BU coins. Probably few are aware of the stories behind the four top gems. They all share the following characteristics:

1. Very low mintage, especially for silver coins of these sizes. Year of Children, Volleyball and Soccer only had a mintage of 1,000. Among proof silver coins of this size, only the Sitting Song Qingling can be their match. Alpine Skiing is even less, to our dismay. The mintage is said to be 500, but it is extremely elusive internationally. As far as I know, only the senior collector Mr. Li Kaoming in Taiwan has a genuine specimen of this coin.

2. Except for Alpine Skiing, the other three top gems were distributed by Paramount in the USA. Also, the actual minting year was 1988, 8 years after the proof Year of Children coin was officially released. The fact that there was a huge gap between the year on the coin and the actual production year will enable these three gems to be remembered forever in history. In contrast, the biggest gap between the year on the coin and the actual production year among proof silver coins is 5 years: The 1992 Ancient Inventions and Discoveries kilo silver coins were actually minted in 1997.

3. When the three top gems (excluding Alpine Skiing) first began to backflow from abroad, they were priced similarly to their brethren with mirror fields, or even less. For example, as close as in 2002 and 2003, the sand blasted Soccer was priced around 500 Yuan, and the sand blasted Volleyball was more regularly seen. Even the sand blasted Year of Children was priced between mere 800 to 1,000 Yuan. These top gems were absolutely not worshipped by coin collectors then. They hardly had their respect.

4. These four top gems represent an unforgettable episode in the history of gold and silver coin releases from our country. Why did Paramount pick out the three top gems and release them in the sand blasted version? Why the Two Players Passing the Ball was selected, but the Single Player Controlling the Ball was ignored? Who was the distributor of the sand blasted Alpine Skiing coin? What was the process of its release? Why only these four top gems?

Probably we will never have answers to these questions. But just because of all these mysteries, prices of these four top gems will sky-rocket.

However, as the four top gems are highly priced, their older brothers from the same origin—the mirror coins with identical designs—would feel indignant and wronged by fate. How come after their release, these more favored rivals should come on the scene?

As a result, there have been cases where the big brother from the same origin is disguised as the top gems by way of some tricks, which makes our hair stand on end.

We all know that silver coins with mirror fields are in fact very delicate. If they are treated with potassium sulfide solution, they will immediately take on the appearance of ancient silver. But what if an old hand treats them with nitric acid of the right concentration? The answer is erosion. The mirror field is eroded, changing into the looks of fake sand blasted coins. The so-called sand blasted Alpine Skiing coins at the Lugong Market in Shanghai were fabricated this way.

But when placed next to the genuine coins, the fakes are readily exposed. First, the genuine coins have mint luster, and when the sand blasted coins are turned 360 degrees, the mint luster will show the effect of concentric circles growing larger and larger. Secondly, the fake coin is dull, which cannot reflect any light, like a fresh and juicy green pepper losing water and becoming a withered yellow pepper in the end. Thirdly, the fake coin gives a flawless appearance, because the nitric acid completely flattens the surface of the coin. But this is where it is betrayed, because genuine sand blasted coins have an uneven surface due to the technological process.

If you happen to run into these four top gems, be sure to stay focused and hold your breath. You feel the urge to act, but need to restrain yourself. Slow down, observe closely and carefully, and then pounce on it. There is no room for indecision.

These four top gems popped up frequently in the Lugong market a couple of years ago. And many coin dealers had a headache selling them. But now they are long gone from Lugong, and collectors can only view them with lingering regret at auctions.

We now all understand why among early silver coins, sand blasted BU coins are superior to proof silver coins of the same design. But there are exceptions: for example, the 1986 China Empress is said to have a proof version, which is a top gem. It is different from the sand blasted BU coin in that:

1. The sails on the junk on the proof coin are wide, while those on the sand blasted coin are narrow.

2. The text on the proof coin is “Commemorate the Maiden Voyage to China by the Junk Empress”, while that on the sand blasted version is “China Empress Junk from America.”

3. The ship’s hull is perpendicular to the sight of the viewer on the proof coin, while the hull is almost parallel to the viewer’s sight on the sand blasted version.

The proof version of the China Empress coin is an extreme rarity.

Talking about the four top gems reminds me of the first modern Chinese silver coin, the mirror Year of Children. Veterans of Shanghai Mint only have good words for this coin, claiming its mirror fields as the pinnacle among silver coins from the PRC. Why?

It was because the early production of gold and silver coins in China was a political assignment, an endeavor to boost the honor and reputation of the country. Many in Shanghai Mint and Shenyang Mint were inspired by this lofty sense and lost themselves in the production. The result was a stream of gem coins.

Here is an example. Why are the mirror fields on the silver proof Year of Children coin so bright and even? It was because Shanghai Mint used three smooth planes in grinding, to ensure absolute evenness of the flat surface. If two planes grind against each other, there is no guarantee that all the unevenness will be removed. Three planes grinding together led to the birth of the exemplary mirror fields among silver coins from the PRC—1979 Year of Children.

However, three planes grinding together are much too meticulous, leading to prolonged production time. So Shanghai Mint changed the rules later on, to save production time whenever they could. From then on, the quality of mirror fields began to slip, and the well-known line in the trade “proof coins are not proof enough, and BU coins are more than BU” started to go around right about that time.

Time flew by and up came the new millennium. Shanghai Mint won the bid for the Dunhuang Cave Discovery project that year. To ensure that the mirror fields were flawless, they started to experiment with three planes grinding together, not knowing that the older generation mastered the technology some 20 years back. Luckily, the Dunhuang coins shot to fame, restoring the reputation of Shanghai Mint. It is interesting to watch the change of fate. All things under the sun are in samsara.

To be honest, the machines for minting precious metal coins are more and more sophisticated these days. In terms of hardware, the simple equipment of the early years was no match. But the “software” of those years was unprecedented: expertise in design, engraving and technical process, in addition to the strong determination in production to defend the honor. It is not true that we can always claim that today’s coins are superior in workmanship to those in the early years.

To summarize: The key to enjoy coins is the word “enjoy.” There are many levels of enjoyment. If coin knowledge is the boat, coins are food, coin collection ethics is our spiritual support, then understanding the technical process of coin making is like a life jacket. With all these, we can brave the waves and head for the ocean of coins.

Thanks, everyone.


  1. Dear Frank, about the 1986 Sun Yat-Sen 27 grams silver, I feel the same special sand blasting effect on the 1993 27 grams silver Mao Zedong's head portrait. Figures look alive!

  2. Do you know if the same technical minting process was used for both coins?


    1. I really do not know. But I would imagine that Shanghai Mint would have applied their best technology on the Mao Zedong coin since it must have been a political assignment for them.