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Archive for the ‘Die Casting’ Category

YOU will have to learn a few words that may be new to you to differentiate struck from cast medals. One of these words is meniscus.  If you look up this word in a dictionary you will probably find an illustration of two tubes, one filled with water, one filled with mercury. The surface of the water is concave. The surface of mercury is convex – that is, bowed down at the edges from a higher center.

Cast metal is like mercury. Metal has the same physical property as mercury that makes it bow at the edges in unrestricted form. Cast metal cannot fill tiny cavities in a medal die design because the meniscus prevents the liquefied cast metal from flowing into these small corners. Thus it cannot reproduce sharp, crisp edges at the juncture of two surfaces.

The most obvious evidence of this can be found where the top of lettering meets the sides, another location is where the rise of relief meets the background or field of a coin or medal. With typical casting, the human eye perceives these edges and corners as “soft.” Under magnification, relief, particularly lettering, appears with “rounded” junctures.

Some medalists were skilled at purposefully modeling soft texture and soft lettering. Louis Roty in France was one. Victor Brenner in America was another. Medallists not as skilled may produce edges of relief that will look indistinct and amateurish.

Collectors, it should be noted, seem to prefer sharp, crisp edges because this is closest to the uncirculated state of a coin. Once wear begins, the sharp edges, like highpoints, disappear.

For a coin or medal struck by a die, the metal fills these junctures and tiny cavities by the force of the die during striking. Struck pieces therefore can have sharp, crisp corners and edges where the junctures of two surfaces may come to a point.

Diestruck pieces will appear sharp and not rounded if that characteristic is in the die. (But here, again, the roundness may be modeled into the pattern and reproduced in the die, or, the piece may have circulated and become worn.)

[The sharpness of the rim / edge juncture, as on proof coins, is something else. This comes from the amount of metal mass in the planchet and the amount of pressure applied, not from any modeling or anything in the pattern.]

A second term to learn is porosity. The surface of a cast piece may appear to have tiny pores or pockholes. These vary in size and are caused by dust or dirt in the mold or from trapped air.

When casting, skillful molders will blast the mold with compressed air to remove all contaminants just before pouring the metal. (Prior to this the mold may even be chemically cleaned.)

Trapped air bubbles prevent metal from filling all the nooks and crannies in the mold. This trapped gas tends to congregate around the base of relief or letters on the field or background. Skillful molders like to mold in a vacuum, or tip the mold and lightly tap it to let the air escape, or make elaborate vents for the air to flow out as the metal flows in.

Humorously, these pores or holes are called “craters” like bomb craters. (I say in my best Yosemite Sam cartoon voice imitation “That’s a figure of speech, Son. I say, that’s a hyperbole. That’s an overstatement, I say, to make them tiny holes look extreme!”)

If porosity is present on the piece you are examining, there is a strong chance the piece was cast. (“I say it was cast, Son. Take my word for it!” Enough Sam.)

In contrast to craters are nodules. These are raised lumps, also called bosses. (I won’t even crack a joke on that – make up your own lumpy boss remark!)

Nodules also result from dirt or trapped air occurring in a previous generation in the casting process. They formed when the mold was made. Now use that pockmarked mold and you get raised nodules where tiny craters were located.

Pieces struck from rusted dies will also exhibit nodules. Here again, these will congregate around the base of relief or letters. This is where moisture settled and attacked the iron metal when the die was stored. Prolonged exposure to a moist atmosphere creates rusting of unprotected steel dies. (Even storing dies one on top of the other with a struck piece between prevents rust, as well as other methods.)

Only with experience comes the ability to identify nodules from poor casting techniques versus nodules from rusted dies on struck pieces. I didn’t say this was going to be easy. Casting nodules are usually smooth; rust nodules are usually jagged and uneven.

Next term to learn: chased. It is so common for cast items to have porosity and nodules formed that they are most often CHASED – hand tooled to remove these tiny imperfections. The term is almost one word: cast and chased. (Can you say “castandchased” as one word?) In some cases you can still see the tool marks, even though the CHASER has a toolbox full of tools (like burnishers) to smooth the metal surface after any gross amount of metal is removed or moved around during chasing.

The busiest worker in any foundry is the CHASER – cleaning up after the cast piece is broken out from the mold. All those casting flaws should be removed and all surfaces smoothed where they are supposed to be smooth. For cast medals the trick is not to remove any DETAIL, to retain all the MODULATED RELIEF, keeping it intact.

The next term may be familiar. It is resonance. That is the sound a coin or medal makes when lightly tapped on its edge. The tone or clarity is caused by the metal alloy, absence of trapped air internally and its thickness. A cast piece will tend to have a lower-pitched sound, a “dull thud,” in comparison to a similar struck piece which produces more of a “ring” of greater clarity and higher pitch.

A ring test, however, is not exclusive or foolproof. A suspect piece should be compared with known specimens if you are testing for genuineness. Both struck and cast pieces will ring – after all, bells are made by casting. The only difference is the resonance. Have you got a good ear for pitch and tone?

A last term to be familiar with is a form of casting, but its results are sharper than even a struck piece. That term is electroforming. This is how numismatic electrotypes are made. These are made in an electrolytic tank where the metal is deposited on a pattern, one ion of metal at a time.

Thus electroforms are noted for their sharpness, plus their extreme fidelity to their pattern, far more so than diestruck pieces. This sharpness has to be in the model, obviously. Electroforming reproduces exactly the surface of the model. This is why electroforming – creating galvanos – were used for over a century for coin and medal patterns (and reduced on the die-engraving pantograph like the Janvier reducing machine).

Here are the three methods of producing a coin or medal and the sharpness of detailed relief each method can reproduce:

Casting

Detail reproducible down to a hundredth of an inch.

Striking

Detail reproducible down to a thousandth of an inch.

Electroforming

Detail reproducible down to the width of a molecule.

The following table summarizes criteria for visual inspection. If you have access to a lot of scientific equipment, you can examine the surface substructure of the metal or you can take microphoto- graphs. There you will see how different struck metal is from cast metal after it undergoes the stress of striking.

Struck vs. Cast Diagnostics by Inspection

Property Struck Cast
Relief edges and corner junctures Sharp, crisp, pointed Rounded.
Surface state Smooth, detail where intended, field generally smooth, all relief fully struck up. May have pores or background nodules present, may appear uneven;flat; detail looks “soft.”
Nodules present None; struck from rusted dies if at all. From the cast mold.
Multiple specimens Identical. Pores, nodules may vary in number, size, position on each cast.
Chasing tool marks None. May be present.
Ring test resonance High pitch. Duller tone.
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In 1936 – at the depths of the depression – Medallic Art desperately needed work. The shop was running part time, half days at best. President Clyde C. Trees was seeking medal jobs anywhere he could. He tried not to fire any worker. Instead they worked in the mornings, the workers sent home after processing what little medallic work they had on hand.

One of the jobs Trees was successful in procuring was for Paramont Pictures Corporation, one of the few firms in America that was booming because of the low cost escape the public found in attending the movies. The medal was to show the firm’s president on the obverse to commemorate his silver anniversary, 25 years, in the motion picture field.

Trouble was the film company needed a large quantity of medals in an impossible short time (perhaps also at an extremely low cost!). Instead of losing the job, Trees solution was to try something he had never done before, instead of striking the large medal on his own presses, he subcontracted the job to a die-casting firm.

Die-casting is different from the tradition means of making a medal. Traditionally a medal is struck between dies, then annealed when it becomes work hardened, then struck again as many times as necessary until it brings up the full relief. Some large high relief medals could require six, eight, even ten blows.

Once you set up the pattern in a die-casting machine and keep the metal intake filled with molten metal, you turn on the casting machine; it operates on its own continuously. It could run day and night spewing out high relief casts in one-tenth, one-twentieth the time for normal multiple striking of fine art medals.

Normal medal production is highly labor intensive, more so in pressman’s time for large medals requiring multiple striking. Die-casting requires only an operator to keep filling the metal intake pot. The casting machine does the rest.

Sculptor Pietro Montana prepared the model for the uniface medal bearing the portrait of Adolph Zukor, head of Paramont Pictures. This was furnished to the die-casting firm. I don’t remember the name of this firm, or even if it was mentioned in the files I examined, when I cataloged this medal for Medallic Art Company archives. Vaguely in my mind, this could have been a New Jersey firm.

The medal was cataloged in the 1960s as “36-5,” now it would be recorded as 1936-005. This was not the fifth medal made in 1936. There was no means of knowing their chronological sequence. Instead, it was the fifth medal I archived for a medal to have been made in the year 1936. The medal even bore the date 1937, the 25th year from Zukor’s 1912 entry into the film business.

Fortunately, I did record the quantity produced from data found in the files – 11,883 were delivered to Medallic Art in 1936, 11,250 were furnished to the client. These were all finished in Medallic Art’s shop by lightly silverplating.

It should be mentioned die-casting requires a low-melting point metal composition. More often than not, this is a zinc alloy. As is the Zukor medal. It was a zinc composition lightly silverplated.

Paramount Medal Rim and Reverse

Paramount Medal Rim and Reverse

Next we should mention the 3-inch medal had an unusual edge, more than a half-inch wide. It had six circular bands around the entire circumference. It was hollow inside this multiple-band rim. Inside this was a blank side, no relief, save for two lines of lettering: MEDALLIC ART CO / NEW YORK.

The medal with this unusual rim resembled a Mason jar lid, a name applied to this medal by all who view it. Mention Medallic Art’s “Mason jar lid medal,” and every medalist knows exactly the medal in question.

The lettered name was on the face of the plunger. As a controlled amount of molten metal is shot into the chamber – one side forming the obverse – the plunger forces all the metal into all the cavities of the mold, in effect forming the reverse of the medal. The cast object is then cooled and ejected.

Paramount Plaquette in antique bronze

Paramount Plaquette in antique bronze

That same 1936 year Clyde Trees sold the Paramont Pictures firm a traditional medallic item, also modeled by sculptor Pietro Montana.  This was a uniface horizontal plaquette with a three-quarter standing portrait of Adolph Zukor. Catalog number 1936-032. This was struck in traditional bronze and was also silverplated. Quantity:  400.

It is unknown how the motion picture firm distributed either medallic item. The large quantity of the first possibly suggest the number of movie houses across America. The lower quantity of the second, might suggests friends and employees of the firm. This is undocumented however.

Two years ago a dealer friend sent me the attached photos of one of these medals he had just acquired.  Please tell me what this is, he pleaded. “I have no idea what it is … the way it is here has me stumped.”

My reply was a discourse on why die-casting and the use of zinc is not appropriate for fine art medals. Time has not been kind to his specimen. Zinc deteriorates rapidly. The silverplating clings to the zinc still intact. However, particularly on the back, vast areas of the zinc has deteriorated to the extreme, it has flaked off taking the light coating of silver with it.

The total appearance now is unsightly. The obverse, while it has not been so severely affected, displays a gray nose on the portrait, a high point susceptible to wear and dislodging any silver coating leaving the dull gray zinc undersurface. Refinishing of this piece would have a mixed result. It could be refinished as one color, but the pits where metal flaking off would still be evident.

Paramount Die Cast Medal

Paramount Die Cast Medal

On the internet we see dozens of firms offering their services to produce die-cast medals. These are all made with low-melting point white metal. Such a composition required for die-casting does not have a precise formula. The composition could contain any of the following:  tin, lead, zinc, antimony, copper, bismuth. Tin and some of the others are expensive, lead is not politically correct these days, thus zinc dominates a white metal composition for die-casting.

These die-casting firm show medals with a range of colors. These are applied colors, enamels or pigments. White metal does not take a patina like what can be applied to the traditional medallic metals, bronze and silver. Thus white metal is used today infrequently for any medallic item. It has been more often replaced by aluminum, a medallic composition similar in color and cost.

White metal is quite similar to pewter. Both are like pure tin and lead –  easy to strike. The first medals were struck in white metal in England in 1761. An entire white metal industry arose in England because of the nearby tin mines in Wales and Cornwall. White metal has been called a number of names in various commercial applications, including:  Alpaca, Argentine, Babbitt metal,  Britannia metal (or simply Britannia).

But its use for fine art medals is not satisfactory, as the attached photos document.

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