Getting ready to create the initial silicone mold layer with a coin pressed into a thin wax layer.
Given that I’ve never worked with the Smooth-On Oomo 25 silicon before, having something go wrong was sort of expected, so I didn’t spend too much effort on including sprue and vent channels in the first molding attempt. If it worked, I would have cut them later. I did, however, include the registration marks since those would be difficult to add later. Oh, and I should probably also point out here that the coin being molded here is real 1735 George II penny (or half penny, I’m not 100% sure) and not one of the copies I bought last year.
The first layer separated from molding container.
The initial mix and pour for the fist half of the mold went well and there were no problems demolding. The final product was soft and deformable under light finger pressure, though this was expected. I suspect this might eventually be an issue when it comes time to do an actual casting.
The coin and first layer of the mold made ready for the second layer of silicone.
The actual problem didn’t come until poring the second half of the mold. Not knowing if the second half would stick to the first. I brushed the first half with a light oil and decided to see what would happen.
The result of the first silicone mold attempt - a solid block of silicone.
Now, in case anyone was wondering, yes, I did have both petroleum jelly and talc on hand but I wanted to see if a brushing of oil would be sufficient to keep the two mold halves from sticking together. As it turns out, it was not. The second layer of the silicone stuck to itself so completely it could not be separated from the first. In fact, the layers were so well bonded, there was no real indication where one layer ended and another began. This is actually very useful information for later should I attempt to pour two part mold layers that are not completely flat, like an “L” shape layer for example.
Unable to separate the layers of silicone, the only option left was to cut the coin out.
So, the next step is to try the whole again with petroleum jelly to see what happens. Also, I will probably use about 1/2 of the amount of silicone in the next mold after seeing how deformable the larger blocks are. I had hoped to avoid having to create something like a plaster backing for the silicone, but it seems that even the larger blocks with probably still require some extra support to keep the mold cavity from deforming when the two halves are are clamped together for the casting.
Melting metal for the third pouring session. For some reason, melting ingots you previously made yourself is rather satisfying.
Last Saturday, I decided to try to pour more metal, but this time I wanted to test just how many pours you could get from a mold before it noticeably degraded. Since the cob coins were rather popular at work, and already had 10 pours on that section of the mold already, I decided to make more cobs until I either ran out of pewter, the molds started to visibly degrade, or the flashing became a major problem to clean. In the end, it turned out to be the lack of lighting that ended the pouring that day rather than any of the previously listed conditions, though the flashing had seemed become a noticeable problem after the 20th cumulative pour. After a total of 25 pours I would say that the flashing problem officially became “more of a problem that it was worth” even though the detail of the coin was still quite good and using a series of hand files and Brillo pads to remove the excess metal and clean the coins was taking about 5 minutes each at that point. I admit that does not sound like much time, but when you are thinking about making 100 coins each run, that small amount of time eventually adds up.
Here's a few examples of coins that were made in the third pouring - about a 1/2 pound of cobs, ecus, and sols plus a one pence coin from my own collection (need to copper plate that last one).
Still, while the main objective that day was to see how many pours could be done with a plaster mold, I did more than one mold available of use and decided to pour more a few more French Ecus (and a few Sols) while waiting for the cobs pourings to solidify to see if a broken mold could still be used after being patched. The results were not that good, though I did manage to get a few coins that day, though the amount of effort in cleaning them was clearly in the “not worth it” category.
So, in summary, my advice to you is that once a mold breaks, make a new one rather than repairing it. Also, when you make a plaster mold, plan on only getting about 25 pours before the work involved in cleaning the pieces you are casting starts to noticeably increase.
A copy of a French ecu made in a mold that broke during casting.
This casting was something I decided to do at the last moment before the Dobbs Ferry event, so once again, no great results were expected. Besides, I’m running low on pewter and need to either find more or finally break down and order a few pounds online. Mostly this casting attempt was about trying to see how small I could make the sprue and vent channels to minimize the amount of work required to clean the coins up later. While that part provided a lot of useful information, flaws in the mold creation quickly became apparent to the point that one broke and most will need to be redone due to how most of the coins shifted position too close to the edges of the mold when the plaster was poured. This is disappointing news given that it is taking about two weeks for the molds to fully dry in this humidity.
Last of the 8 reale cobs left from the second casting.
Still, while there were a number of problems with the molds and some temperature issues with the charcoal (I was using a new batch), some usable coins were created out of this small run and were quickly snapped up by people in the group and at work following my progress so far. The unfortunate part was that I forgot to get pictures of the few finished coins that I made.
After getting more plaster, I started making more coin molds. In a few more days I should be able to start turning out large amounts of coins. I suspect that I’m going to need to head back to the local thrift shops and try to find more pewter items to melt down or just break down and order some online.
One problem with casting Rev War era coins is that many of the ones that were in common use were made of copper or silver. The “silver” ones are easy to make using pewter because the metal looks about the same. The copper ones, however, are a bit more of a problem - or were a problem until I ran across this video…
This is nice in that it doesn’t involve any dangerous arsenic-based solutions like gold and silver electroplating processes do. A more complicated setup for copper coating lead bullets can be found here.
I do believe my copper coin problem may be solved.
Yeah! The I ordered online arrived today. All I need now is more plaster. For those that don’t know my ultimate goal with the coin casting, I’m trying to create some souvenirs to give to a few people at the Rev War events our group does (who doesn’t like coins?). Given that each of the coins you can buy online costs about $1 - $2 each (plus shipping and handling), you really can’t afford to give them away for long. BUT, if you made them yourself, all it would cost you is the time you spent making and cleaning the coins plus the cost of the pewter. Besides this is an interesting project than may lead to casting of more useful things in more durable metals.
Eventually, I hope to make a verity of coins that I either designed myself or cast from real coins that I own, but for the moment I’ll work with the few coins that I have on hand.
Done with the first pour - using only gloves was not smart.
I finally got a chance to pour some pewter today in a coin mold that I made a while ago (using various 20th century coins), and I have to say that the results were mixed. The impressions on the coins turned out to be better than expected for using plaster and having the graphite pool over the tops of the coins for some reason. I had thought that the mold was a total loss, but decided to use it anyway to figure out how large the sprue and vent channels needed to be. Besides, I needed to practice pouring anyway, and if the casting was a disaster or the mold broke, I was not expecting much anyway.
It turns out that the results were better than expected. The mold worked OK, but after 10 pours there were noticeable cracks on both sides of the mold that followed the sprue channels. I’m not sure why that happened but internal supports, such as chicken wire mesh, might resolve that issue next time. Later, when the mold cooled, the cracks shrank to being almost unnoticeable.
The first pour was a near disaster, as I seriously underestimated the viscosity of the molten pewter (it pours like water!) and the internal volume of the mold. The result was an overflow that was caught by the cast iron pan I had the mold sitting in (I kinda expected something like this to happen). The rest of the pours were without incident.
Partial result of all that work after cleaning.
As for the coins themselves, most of the mold details were faithfully reproduced from the first pour to the last. Repeated pouring and removing the metal did not cause nearly as much wear on the plaster as I expected. I wish the detail on the front side of the coins was better, but that was a result of an issue when making the second half of the mold. My only real complaint about the coins is the amount of flashing that needed to be removed afterwords due to my sprue and vent channels being larger than what was actually required. Pewter is soft, but even soft metals take time clean up with wire cutters and a file. Voids are also a bit of an issue, but I think that has more to do with pouring temperature and speed. With more practice, I think I can do better.
Plaster test molds with some random coins from my collection. Note how the graphite powder pooled all over the tops of the coins.
Well, it would appear that my most recent attempt at making a coin mold has failed again, though I did manage to get this one to separate. The graphite that I managed to pick up was not fine enough and for some reason pooled on top of the the coins when pouring the second layer. this caused the detail on one side of the coins to be completely lost. Still, this is not the end of the world as I still intend to use the mold anyway to test how many coins I can make before the mold degrades and detail is lost from the one “good” side.
All that’s left to do is wait for it to dry a bit more and cut the sprue and vent channels, then pour some pewter.
