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Cast, Casting

Cast, Casting.  Made from molten metal poured into a mold. Metalcasting is the world's oldest metal technology, spanning more than 5,000 years in man's history, yet it is as modern and necessary as the most recent model or medallic item. The ease in which molding can be done is why artists use this technique to cast designs in their own studios (see also plaster casting) and yet why a giant industry exists for casting metal parts from the size of pins to steamship propellers.

There are several casting techniques – and there has been more development in this field in the last 50 years than in all the previous 5,000. Yet techniques from prehistoric times, as sand casting, are still in common use today.

Patterns for coin and medal designs have been cast in metal (then reduced by pantograph to create dies the required size as small as a dime). Also casting has been used for making the end products, as many cast art medals – and coins from early

China – attest.

In contrast to the foundry casting industry, medallic casting is small by comparison. Coins and medals are small size, their shape is generally flat, and they lack complex forms. They have no undercuts and are the simplest form of relief casting. Medallions larger than six inches – because of the limitations of size in diestriking in presses – are always cast. Medallic objects, often in somewhat more complex form, are usually cast. Thus the medallic field has been casting glyptic objects since Pisanello created the first cast medal in 1438.

Cast Coins, Medals and Plaques

As such, cast coinages have been made – particularly in China where coins were

made by casting several at a time connected to a stem, called a tree. They were placed in use by breaking off the coins as needed. In modern times most cast coins are counterfeit. They are made by permanent mold casting, with molds that can be broken apart for the removal of the cast piece then used to cast again.

Cast medals are somewhat more common and genuine. Such cast medallic items

sometimes have only one side (called single-sided), but may have two sides, (called double sided if both sides are in the mold), or may have two sides where two single-sided cast medals joined together (called cast double). Plaquettes are sometimes cast (if not diestruck), plaques are always cast because of their larger size (over eight inches). Thus plaques, always intended for display, have a flat back with some means for hanging or upright support cast on back.

Cast versus Struck Surfaces

Metal objects that are cast have physical characteristics different from struck objects. The surface of both types is most characteristic. Cast surfaces usually exhibit a grainy appearance, and are more rounded than the sharp angular detail of a struck or coined metal piece.

Generally a cast surface is not completely smooth but may exhibit the roughness

of the surface of the mold or contain pits (blowholes from escaping occluded gas). Struck surfaces are more likely to be smooth with no inherent imperfections.

Cast lettering appears rounded and less distinct. Struck lettering can be sharper and more angular at the top of the letters and where the sides of lettering meet the field.

Casting is a slow operation, but can be speeded up by diecasting, forcing hot

metal into a die mold (but only metals with a low temperature melting point can be

diecast – as white metal zinc alloys). For production runs requiring high production speeds, coins and medals are required to be struck. Diestriking in modern presses is preferred to casting for another important reason – far more intricate detail can be reproduced by dies than by molds.

Cast Counterfeits

Because counterfeiters cannot usually afford the very large expense of die making equipment and stamping presses – in addition to the artistic requirements of the original patterns, dies and tooling – coins are more often counterfeited by casting. Once the counterfeiter has an original coin, making a mold, as mentioned above, is fairly simple. Casting from that mold is also easy, although it will result in several obvious characteristics (which numismatists call diagnostic detail): slightly smaller size than the original (shrinkage), a surface of varying porosity, and a small loss of some detail and definition.

More recently counterfeiters have been making dies or molds by edm  (but this

process has a characteristic pock-marked surface evident under magnification, unlike the smooth surface of conventional die making methods or cast porosity).

   Medallic Casting Techniques

Casting techniques that could be used to make medallic items include lost wax

(also called cire-perdue, waste wax, precision casting  and investment casting); die-cast, diecasting (where metal is shot into permanent molds); shell mold or ceramic mold (with very smooth sides of the mold wall); flexible mold  or rubber mold (for items of high relief and undercuts); and permanent mold casting (for multiple casting). Sand casting is not suitable for medallic work because of the great porosity and inability to cast minute detail.

                                                          

           [Illustrate: NH127 Londonderry Medal]         

                                                         

                      Sand Cast Medals                   

                                                         

       Here is an example of what not to do. An item     

   made by sand casting looks overly crude, rough and    

   sometimes pockmarked. The process cannot reproduce    

   the fine detail, crisp relief and sharp edges of      

   diestriking (or electrogalvanic casting) which gives  

   coins and medals much of their charm. Lettering is    

   particularly vulnerable, as is evidenced here.        

   Modulated relief is greatly limited.                  

                                                          

       The original caster of this piece chose to remain 

   anonymous (perhaps, understandably so.) The artists   

   and sculptor are known, but are not listed here (to   

   save their obvious embarrassment).                    

The intricacy of detail differs widely among these techniques; diecasting is the closest to a diestruck object being able to create detail as small as 1/32nd inch. Sand casting is the least likely to create detail, down to only about 1/10th inch. porosity of the surface – the bane of all casting – differs somewhat with each of these techniques also.

In numismatic cataloging it is not necessary to identify the casting technique used to create a specimen at hand (if, indeed, this could be recognized). It is mandatory, however, to reveal if the specimen was cast, or made by one of the other processes (diestruck pieces do not need to be identified since they are the norm). The sharpness of detail would be one diagnostic for identifying the process of manufacture. Cast items, as explained above, lack this sharpness.

Word List  #7

Casting Terms Explained.

anepigraphic – Without lettering.

carbon spot (Sulphur Spot) – Tiny area of corrosion formed by copper in bronze corroded by exposure to sulphur. "Carbon Spot," formerly used, is actually a misnomer. It should be removed immediately (by chasing) or it will grow.

cast hollow– Not cast solid, made like thick shell.

Casting Flaw – Any imperfection made during casting.

Casting Nodule – A lump or boss of metal formed in a casting from a pit in the mold.  See BOSS.

chasing – Working the surface with tools to remove imperfections, to smooth out and finish up the surface.

electroform – Made by electrodeposition (like thick copper plating).

flange – An extension around a model or pattern (to hold the

work during processing).

galvano – An electroform; made by electrodeposition.

highlight, highlighting – In finishing, using a contrasting color or method to emphasize detail (usually by adding a darker color in the crevices; also called the French Finish).

incuse – Sunken lettering or detail, as cut or stamped into.

inscription – Lettering anywhere except around the perimeter of an item.

Internal LoopLoop made at the same time as the casting; part of the mold.  See integral part.

legend –  Lettering following the perimeter (in contrast to inscription).

listel – A narrow flat straight bar or line separating design elements.

logotype – A punch with entire name on it.

monogram – Letters or symbols indicating the artist's signature, often in artistic arrangement.

Mold Debris – Area of imperfect design not intended by the artist, caused by sloppy casting.

Mold Number – An identification number on a casting.

patina – Surface coloration; a permanent color applied to a metal surface. Cast

                 items always need to be patinated or finished.

plaque – A one-sided work of art in metal, with at least

one dimension greater than eight inches; since

plaques are usually square or rectangular,

circular plaques must be so identified.

plinth – The square or rectangular panel at the base of a

plaque or plaquette; the area below the base

line with square corners; it usually contains

lettering.

porosity – A surface full of tiny pores.

repousse– Creating a relief design by hammering from behind.

Skirt – A bent over edge as on an electroform. See box medal.

truncation – The edge of relief where the design is literally cut off; said of a bust or portrait where the body design ends.

white metal – A base metal composition of zinc or tin with any of several other metals without specific formulation.

wipe marks – A kind of toning which results from a liquid applied with a cloth to

            finish a piece, but which tones in streaks.

Those terms in small caps have entries in this encyclopedia.

References:                                                                                                                                

M3 {1967} Landowski.

M4 {1980} Ammen.

M5 {1981} Kotzin

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor


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