I have normally no interest in subaerat coins (i.e. ancient forgeries). However, this coin was recently sold in an auction (not a coin auction) in Germany. The coin was described as modern forgery and received no bids, so I picked it up for EUR 50,-. I'm quite sure that it is ancient, though.
I don't know for sure. The coin has all sorts of signs of wear and tear. The gold cover is broken in places around the edge (e.g. at 10 o'clock on the reverse). The whole look and feel is ancient to me, but again, it is difficult to say for sure. If anybody has better insights, I would be more than interested to hear about it. In particular, I would be interested to see subaerat solidi of the mid-4th century for comparison.
Not my area of interest, but it does look gilded? The core metal is showing at several places (may be the photo though).
The question is whether the coin was struck in base metal and then gilded or cast and then gilded. Making a struck fake is more work and suggests it might be old but casts are cheaper and could be any time. Are those raised lumps around the edges? I would be intereested in seeing what experts would say if they saw it 'in hand'.
Here is an interesting site if someone wants to know more about fourrées. I enjoyed examining that special collection: http://www.emigh.org/numis/fourree/
My understanding is that a subaerat coin is made by striking, where a gold (or silver) sheet is placed over a core of copper or some other base metal. I think this is exactly how my coin was made. It was certaintly not "gilded", i.e. the golden outer layer was not applied after the coin was struck.
That is right, the core (I think copper) is showing in several places around the edge. But the coin was not gilded, by applying a thin layer of gold post-striking, but the gold-sheet and the core were struck together into the coin. The coin is also way too heavy. My unreliable Chinse scales said 6.8 grams. Note the big excess rim, which I think makes no sense on a genuine official gold coin. I think it is possible, that the coin was struck from official dies. The strange rendering of the Letter R, which can be similar to N and A, can also be seen on official examples. But again, I'm not sure. This coins below were the model: https://www.acsearch.info/search.html?id=678550 https://www.acsearch.info/search.html?id=1914194 This one was sold for 440 Swiss Francs (some 440 USD) in 2000. I would take it at this price: https://www.acsearch.info/search.html?id=73820
I just had a good look at the lettering. The coin is probably not from official dies. The rendering of some letters is very strange indeed. As I wrote before, the letter R is sometimes an A (with and without square bar) or an N. The R on official coins also looks strange sometimes, but the forger probably took it a bit too far. When I bought this coin in a (non-numismatic) auction, I took it home and stashed it away, since I don't really like subaerate coins. However, on second thoughts, this is actually quite a nice thing, given that I will probably never own an official solidus of Julian. Also, I am quite convinced that the piece is an ancient forgery made in the 4th century to deceive maybe by mixing it in among a larger sum of official coins.
Does it really weigh 6.8g? If it's an ancient fake then it's a poorly made fake indeed. Such a high weight of 6.8g will have stood out for sure, even by casual handling.
I shall re-check the weight. My Chinese scales are not reliable. If I put a coin on it, the displayed weight usually adjusts for as long as I leave it on the scales. But then again, the piece is heavy with all the excess metal on the edge, and it is unusually thick as well. As for detectability, I think ancient forgeries were often passed on by mixing them into large payments, which could not be checked thoroughly on the spot. Gold was usually used to pay taxes and to pay soldiers, including barbarian auxiliaries and federates. Mixing a couple of these into a payment of say 3000 solidi for a unit of federate Gothic warriors may have been a nice little scheme to reduce the costs of their service. While they may not have been able to verify the authenticity of all the coins in the payment (and in fact may have liked the heavy ones most). In fact, a lot of subaerate solidi have been found in Ukraine, where the Goths lived at the time.
Just to add on. You can search for fourree solidi on acsearch. There are no fourrees on acsearch for Julian, but there are for his contemporaries, Constantius II, Valens, Valentinian. All the examples I skimmed through weigh less than the official weight of 4.5g. Not more.
That is interesting to know. I'll recheck the weight on mine, but I'm sure that it is on the heavy side. I suppose with some fourrees a low weight could result from a corrosion of the core. Otherwise, there is no real reason for the forger to deliberately undershoot the weight, since the copper or bronze core is cheap.
One huge problem of gold fourrees is that specific weight of gold is 19.3 grams per cubic centimeter and of copper 8.9 grams. The forgers can achieve that the fourrees with copper core have same weight as offical coins from pure gold but then this fouree will have a much huger size or a much thicker planchet, because copper is much lighter than gold! If they want the fourrees to have same size and thickness of planchet like real offical coins from pure gold, than the weight of the fourre will be much lighter because gold is much heavier than copper. The specific weight of gold is 19.3 grams per cubic centimeter; it is the sixth heaviest metal. For comparison: lead weighs 11.4 grams per cubic centimeter, iron 7.9 grams and copper 8.9 grams. If the coin like here weighs much more than it should it would mean that the planchet must be extremely thick that it would have been very obvious to anyone in the past that the coin must be fake. If you place it next to a real offical coin you would have noticed it immedialtely or anyone who every handles a real one must have noticed. So to mix it with real coins would make the problems even more obvious because you will then have real coins for comparison. Making the coin heavier means to make the planchet even thicker and so to make the fouree even more obvious. Not sure if people were really that stupid in the past. I think best way was to make the fourre a little bit lighter and the planchet thicker, that the fourre will not be noticed that easily.
They knew in ancient times already about the different density of gold , silver and copper. See for example the very famous story about Amchimedes, who chaught the goldsmith, who mixed base metal into the crown for king Hieron II. We had this early in school, so I remembered this story well especially because he said in this context "heureka". He did the crown in water and determined how much the water rised then gold with same weight and determined how much the water rised. The water rised more when he did the crown in showing that the crown could not be made of pure gold. https://www.math.nyu.edu/~crorres/Archimedes/Crown/CrownIntro.html
I put the coin on my scales again and let it fully adjust. The final weight came in at a whopping 7.05 grams. The flan is clearly too large for the dies and the coin is thicker than an official solidus. The metal core is silver-grey. It is definitely not copper or bronze. The gold cover is quite thick. It was folded over the core from the obverse to the reverse. The fold-over edges can be seen at 1 to 2 o'clock on the reverse. I searched acsearch and could not find another subaerate soldius that was overweight. In fact, as a rule they are underweight. So in short, I have no idea what the idea was with this coin. Maybe the forger was completely indifferent to the weight.
