Sand and Clay Mold Castings
Sand and clay mold castings are probably the least dangerous of cast forgeries, as the fakes made this way are normally of such poor quality that even novice collectors can learn to spot them easily. Such fakes are inexpensive and easy to make, and are generally intended for the tourist market.
A box is constructed in halves that fit together easily and are filled with fine sand or clay mixed with a binding agent that holds the grains together while remaining soft. The coin to be copied is impressed into the sand on each half, and a channel is cut from the edge of the coin to the edge of the box (this is known as the sprew channel) so that when the two halves of the box are fitted together a mold is created. Molten metal is poured into the sprew channel to fill the mold. The result is a copy of the original coin with a metal "sprew" attached which is then cut off to leave just the coin. Each casting requires new impressions in the mold, but it can be done very quickly. Also, each molding can have more than one coin impressed so that multiple examples can be made with each pour.
There are several problems with this method that make such fakes fairly easy to spot :
1). It is difficult to fit the mold halves together perfectly and any gaps result in metal leaking into the gaps forming what is commonly known as a casting seam, which may go either all or part way around the coin. The casting seam below is actually on a lost-wax casting, but gives the idea of what one might look like on a sand casting.
Casting seams on sand casts are usually more pronounced so have to be filed off or left very visible, and it is very difficult to remove them without leaving obvious marks on the edge. Below is an image of an edge filed to remove a casting seam, but keep in mind this one is much more obvious than most will be, and some coins will have the edges "worried" to try to hide these marks.
One thing to keep in mind is that there are a few types of genuine ancient bronze coins with filed edges, due to how the blank flans on which the coins are struck were made. This is especially true for some bronze coins from Phoenicia (around Tyre) and most Ptolemaic bronzes after Ptolemy I. Before condemning a coin because of filed edges, be sure of your facts, and ask someone with experience to advise you if you think the coin you are looking at might be one of the exceptions.
2) Often, the two halves of the mold do not match up perfectly, so that one side of the coin will be slightly offset from the other, generally with the offset running around the rim of the coin. Such offsets are technically a type of casting seam, but are more dramatic and virtually impossible to hide.
3) The sprew has to be fairly large because the molds are normally used cold, and if the channel is too small the metal will solidify before filling the mold. The sprew must be removed by either cutting or filing, which normally leaves marks on the edges.
4) The sand grains leave impressions in the surfaces, resulting in a textured surface that does not look at all like that on an original coin. One can clearly see such sand grain impressions on this cast Balbinus sestertius.
5) Sandcasting is a coarse method, normally with considerable loss of detail in the process. Coins made by this method will generally be somewhat muted looking, as well as grainy.
All of these problems except for the loss of detail can be overcome by "worrying" the surfaces and edges, but anyone that would go to that much trouble would probably have chosen a better method of forgery, anyway.
Re-usable Metal molds
Corinthian Metal mold Fakes
Many common reproductions made for giftware and never intending to fool collectors, are made in two-piece re-usable metal molds. The process is the same as used to make home-cast toy lead soldiers with an impression of the two sides of the coin on iron or aluminum molds that fit together easily so that molten metal can be poured in through a sprew channel. The advantage of this method over sand casting, is that the molds are re-usable, and hundreds or even thousands of coins can be cast very quickly with just one set of molds.
The advantage of this method over sand casting is that there are no sand grains to leave impressions on the surface, so the metal tends to have a smoother more natural look. However, it shares some problems in that there will be a sprew that has to be removed, a mold line will normally be visible around the edge and may need to be removed, and since it is even more difficult to get a fit between the parts of the mold, significant amounts of metal may squeeze out between them leaving "flashings" of extra metal on the mold lines. You can clearly see such a "flashing" on the lower of the two images above.
An additional problem is that metal molds are normally used cold but conduct heat quickly. This can cause molten metals with high melting points to solidify before fully filling the molds, resulting in an incomplete casting. This makes casting in silver, gold or bronze somewhat unsuitable for this method, so metals like tin, lead or zinc with low melting points are normally used and must be plated with another metal to have any chance of deceiving. Another problem is all coins cast from the same re-usable mold will be so similar to each other that two placed side by side (as in the images above) will be very obviously from the same mold. Any time you see two ancient coins that are that identical, you should realize immediately something may be wrong and investigate further.
This fake Corinthian stater is a very commonly encountered metal mold cast fake and is of base metal alloy plated with chrome. While not absolutely identical, there is no question both were cast in the same mold. These were made for the giftware and museum replica markets, and never intended to fool an experienced collector, although they can fool some novices and we get numerous emails from people sending images of them and asking what their "genuine ancient coin" is worth.
Lost Wax Castings
lost wax cast fake
Lost wax castings can be much more dangerous to collectors, but require correspondingly more sophisticated equipment to make. This is a method commonly used by jewelers to make gold and silver jewelry so the equipment is readily available. Fakes made by this method are normally aimed at deceiving, although some are intended only for the jewelry market.
This is a two-step molding process and there are a few ways to make the first mold, but the most common is to paint a genuine ancient coin with a rubber compound which captures details very accurately. The rubber is vulcanized and then cut in such a way as to allow the coin to be removed but the cuts will fit back together very closely. A small sprew channel is cut, into which hot wax is injected to create very accurate wax copies of the original coin. The wax copy can be removed through the same cut the original coin was. This rubber mold can be used to make large numbers of identical wax copies of the original coin.
While the waxes created from one mold are all identical and often have small casting seams where wax leaked out at the cuts in the rubber, wax is very easy to manipulate to remove the casting seams, build up or cut down edges to change the outline of the coin, or modify small details so that they are not all absolutely identical.
The wax copies are then fitted with a fine wax sprew an inch or so long, placed in a short metal tube with the sprew sticking out. A substance similar to plaster-of-paris, known as "investment", is poured in to encase the wax with the sprew projecting out. When the investment hardens and dries, the tube is placed upside down in a hot kiln until the wax melts and burns out (hence the name lost-wax) leaving a cavity the exact shape of the coin, and the channel left by the wax sprew provides a channel leading down from the surface of the mold.
While the mold is still hot from the kiln, molten metal is poured down the sprew channel to fill the cavity, creating a fairly accurate copy of the original coin. There are ways using steam, or just centrifugal force by spinning the mold, to force the metal more compactly into the mold, resulting in better details on the finished coin. As soon as the metal solidifies, and while the mold is still hot, it is thrown into cold water causing the investment to break up, and the coin just falls out. The sprew is then cut from the coin and the coin is basically finished, although minor "worrying" may be used to hide the sprew removal point and other signs of casting by this method.
Fakes made by this method can be of much higher quality than sand casts for several reasons:
1) While a casting seam will normally be present on the wax copies, it is easily removed from the wax without a significant trace (although this is not always done). No casting seam is created in the final "investment" process, so fakes made by lost wax casting often show no visible casting seam.
2) The sprews are much thinner than on sand casts, so removing them and "worrying" the area to remove any sign of them is much easier, although one can often figure out where the sprew was.
3) While casting quality varies, if good quality equipment with pressure or force to compact the metal into the mold is used, coins made by this method can have very good surfaces and capture very fine details.
However, there are also some technical problems that are difficult to overcome:
1) While painting the rubber onto the original coins, air bubbles can become trapped in finer details on the coin. These air bubbles act like part of the coin's surface and result in depressions in the rubber that become round bumps on the waxes made in such molds. These bumps will then be present on the finished coin and are what are sometimes referred to as "casting bubbles".
2) As the wax is injected into the rubber molds, again, tiny air bubbles can be trapped but this time they act as part of the mold and cause depressions in the wax that will show up on the finished coins as rounded depressions on the coin. They are sometimes referred to as "casting porosity".
3) As the wax is immersed in the investment, again, tiny air bubbles can be trapped which act as part of the wax to leave depressions in the investment, which will result in small bumps of extra metal on the surface of the finished casting (casting bubbles).
4) As the metal is poured in for the final molding, again, small air bubbles can become trapped which act as part of the investment and show up as depressions (casting porosity) on the finished coin.
There are so many steps at which air can be trapped to create casting bubbles or porosity, that the majority of lost wax castings are going to show some evidence of it if you look closely. The example illustrated above has many small raised bumps, most clearly visible immediately in front of the chin with one big one in the upper left at about 11 o'clock. There are also several small depressed areas clearly visible on the cheek. These are all the result of air bubbles trapped at various stages of the process. Remember that this image is greatly enlarged, and these feature will often be visible only under magnification. There are a few reasons that bumps and depressions may be found on genuine coins, so when you see them they are reason to examine a coin much more closely, not reason to condemn it out of hand.
5) Another major problem results from material expanding slightly when hot, and then shrinking as it cools. As a result, when the hot wax is poured into the rubber mold it fully fills the mold but then shrinks slightly as it cools. The amount of shrinkage is minor and the wax is only slightly smaller than the original coin. The same thing happens when molten metal is poured into the investment mold and then shrinks as it cools. Not only was the wax slightly smaller than the original coin, the finished fake is again slightly smaller than the wax. Due to the two stages magnifying each other, an average lost-wax casting will be about 18% lighter than the original coin used to make the rubber mold. There are measures that can be taken to reduce this problem, but they are difficult to control, and accurate weights via lost-wax casting is difficult. For genuine coins that have very consistent weights, a good set of scales accurate to at least 0.1 gram is an important tool in spotting some types of fakes. Via this link you can see a Chios didrachm recorded in our examples section, which is 22% too light for the issue, not far from the 18% lost wax castings average (and if the original coin copied was at the low end of the weight standard for the issue it might be exactly 18% less).
6) A further problem which was mentioned above, is that every wax produced from the same rubber mold will be almost identical. Wax can be easily manipulated to add or remove wax around the edges to change the outlines, or to add or remove minor details, but any attempt to modify major details will not be very convincing. As a result, although two lost wax coins from the same mold may have minor differences, the similarities will be so strong that they will be fairly obvious when two coins appear to have been made in the same mold.
The coins illustrated here were sold on ebay by the "Toronto Group" forgers who have plagued eBay for the past couple of years and still show up once in a while (we chose this example because one of this exact forgery was sold on eBay by a seller in Europe the day we were writing this). The edges may be slightly different, but the waxes for these fake Macrinus denarii were all obviously made in the same rubber mold.
7) No molding process is perfect, so there is always minor loss of detail between the original and the fake, and smaller details are more likely to be lost or muted. The very fine details are created as flows into a die during striking, which give a die struck coin the look of having been die-struck, and are generally too small to be captured by this method. This is why fakes made by the lost-wax method normally do not have that "die-struck" look of genuine coins. With experience one can learn to recognize such fakes just by their look.
8) As discussed above, tiny air bubbles are likely to get trapped in the molding at various stages. Many of these bubbles are too small to see and you will not know they are there, but the microscopic surface textures they create are very different from those on die-struck and aged coins, and you can often feel the difference. Cast coins tend to have a "soapy" feel cause by microscopic rounded bumps created by these bubbled, which is why many cast coins simply do not feel right. Again, learning to recognize this comes from experience.
After you have handled enough genuine ancient coins, one day you will pick up a cast fake, and know something is wrong. It will not feel or look right, and that is the time to take out your microscope and give the coin a very careful examination for signs of casting. Even worn coins will usually have traces of the original struck surfaces in protected areas (such as the insides of letters) and will show some evidence of having been die struck. Unfortunately you will have to handle and examine tens of thousands of genuine coins before this becomes second nature, and most collectors will never have the opportunity to handle that many coins. Be very careful, as this is an area where a little knowledge can be dangerous, and unless you study enough examples, you can easily make a mistake and condemn a genuine coin that has been over-cleaned and all traces of the original surfaces removed.
Some of the forgers have dramatically improved the speed with which they can make latex molds and from them the waxes needed for their lost wax castings, and they are using high pressure casting techniques, which have improved both the speed at which they have made the coins, and the quality of the castings. It seems to be economical for them to make a mold and only a very tiny number of copies, of even inexpensive types that people might over look in larger lots of coins. But they still cannot capture the microscopic details that make die-struck coins look and feel like die-struck coins, and give them their lustre.
There are some fairly good diagnostics that allow these types of fakes to be detected, but at this time we do not have any specimens on hand to image to illustrate them. We will eventually get those specimens and will provide that information at that time. In the meantime, one of the things we have noticed with them is that they tend to have a soft muted appearance that resembles coins that have been over-cleaned in acids. For the most part, they are forging silver coins with this method, and we would suggest that until you get a good handle on what the fakes actually look like, it is best to avoid any coin that has a soft, slightly acid-washed or over-cleaned look to it.
There is a new book out, specifically on these and other cast fakes coming from Bulgaria, and you will be amazed at the types of coins being forged there by this method. The book is CAST FORGERIES OF CLASSICAL COINS FROM BULGARIA by Ilya Prokopov and Eugeni Paunov, which can be ordered from the SP-P Publishing house website. When we looked at this book our first reaction based on the images was that many of the coins looked to be genuine, and we were not impressed with the authors descriptions of what was wrong with the coins (too vague to be useful) but once we had a chance to examine some specimens for ourselves (including one coin we bought as genuine from a another dealer at a coin show and only later came to understand what it was and returned to him), we came to realize that the authors of this book were absolutely correct. In spite of the book's flaws, we still highly recommend it.
A General Problem With Castings
Many genuine ancient coins develop flan cracks due to metal stress during striking, and while castings can easily capture the surface features of these cracks, they have great difficulty capturing the internal structure of them. For purposes of detecting fake coins, this will only be useful if the original coin had a flan crack of which surface evidence is visible on the fake. This will happen often, but not all genuine ancient coins had such cracks (ie. the absence of this feature does not prove a coin authentic). Also, the better the casting method, the more internal details of the flan crack will be copied, but no casting method can capture the internal details of the finest flan cracks. Have a look at this Germanicus bronze:
The first thing you should notice is the very soft appearance for a coin of this grade. This is the first clue that you may be dealing with a cast fake and should look closer (in this case you are looking at a 19th century lost-wax casting). There is clear evidence of a flan crack at 2 o'clock on the reverse, and while it is not as obvious on the image there is evidence for the same flan crack extending through to the obverse (it is more obvious with the coin in hand). Here is a better look:
Any flan crack that goes through the coin from one side to the other has to be open within the coin in such a way as to be wedge shaped; widest at the edge and narrow as it goes deeper into the coin. Examining the edge should show clear evidence of it, so why is there no trace of it in this coin's edge?:
When this fake was cast there probably were traces of the crack visible on the edge, but the edges of this coin were "worried" to remove evidence of a casting seam (traces of which are visible elsewhere on the coin), and during that process all traces of the crack were removed. Since the actual crack on the original genuine coin had to extend as far into the coin as the length of the crack visible on the reverse (about 2.8 mm), light filing of the edge of the original would not have completely removed it like this. This is clear proof that this coin is not genuine.
Here is a similar, but genuine shallow flan crack clearly complete across the rim, joining those seen on the obverse and reverse surfaces. This example is slightly masked by encrustations in the crack, so I will replace it with a better example as one becomes available. I think this one still makes the point.
This is not unique to cast fakes. The same problem can exist for some die-struck fakes, when in transferring the image of the original coin to a false die the features of a crack are captured. Such false dies will transfer those surface features to a coin struck from them, but cannot create the internal structure of the crack at that exact place.
It is also important to note that the higher the quality of the original molding, the more of the internal structure of the crack will be captured. This example above is very dramatic and illustrates the principle well, but modern very high quality castings now coming from Bulgaria can capture the wider parts of the edge cracks and one must look closely where they narrow down to see if they are open there. Hopefully we will get good images to illustrate this sometime in the not too distant future. You will need a good magnifying glass or microscope to make this determination on the best fakes.
Next page: Electro-Types