Choices (An introduction)
So the first question: why metal? Short answer: I don’t like resin. Slightly longer answer: Resin also has arguably long curing times and moulds wear out rather quickly – which is expensive in the long run. This would be fine for a few casts but I would be forced to look for alternatives when casting a whole army. Resin also sounds annoying to handle, store and dispose of and is apparently susceptible to environmental factors such as humidity and temperature while curing. I don’t see dedicated equipment such as a pressure / vacuum pot as a big disadvantage as metal casting also requires its own equipment.
Metal miniatures are traditionally cast in either vulcanized rubber or silicone, usually with the aforementioned spin-casting technique. Here, centrifugal motion forces the molten pewter into the mould allowing for more intricate designs. Spin-casting machines however are expensive and I am not yet willing enough to build one myself. The main advantage are the high throughput and more complex designs you can cast. Gravity casting is possible as well, however and Admiral told me that at least one of the companies he worked with use this technique. Knowing the limitations of gravity casting, I designed my miniatures as compact as possible.
I also want to add at this point that you can decide to use either leaded or lead-free pewter. Leaded pewter has arguably better flowing characteristics and a lower melting point which in fact seems so easy that almost everyone is able to do that (keyword: Prince August). Leaded pewter also contains… well… lead (these days usually <15% – just to put this into perspective: many brasses, steels and aluminium alloys also have a low percentage lead content). Interesting history lesson I learned while researching alloys: the US has effectively outlawed lead in miniatures in the early 90s (around 1991-1992) forcing US GW there to adapt much earlier while they continued until late 1997/1998 to use lead in miniatures sold on the European market. They had a short transition phase where they experimented a bit with alloys (my 2nd edition Necrons look different to earlier and later miniatures) before they settled on the white metal alloy they use to this day. I settled on the potentially more difficult lead-free route, more specifically the alloy Sn95Sb4Cu1 (more on alloys in a later post) – if it goes well there is little reason for me to change alloys and if not I can still think about the alternatives. A quick note on metal prices. Since the beginning of the Covid pandemic, raw tin prices have tripled. If this trend continues, resins or thermoplastics may become more attractive for miniature manufacturers. I bought my alloy days before the all time peak in early March (sigh) from a local company specialising in casting materials.
Next, we need to decide on the mould material. A quick internet survey seems to suggest to use two-part silicones, so called room-temperature vulcanizing (RTV) silicones, more specifically variants that are designed for casting metals (Smooth On’s Mold Max 60 for example – conveniently, these silicones are often red but I don’t know if this is convention or due to additives such as iron oxide). Their advantage is that they don’t need a vulcanizer. This is a device that evenly delivers both heat and pressure to cure the moulds. Their disadvantages are that they are susceptible to entrap bubbles (and bubbles in moulds are arguably worse than in the model). So you need to make sure to adequately degas them (or compress the bubbles – I always forget which one is the one you want to use with silicone). If you go the resin route, chances are, you already bought similar equipment for removing bubbles from the pours but for me, that would imply more costly equipment. The industry also does not use them and I suspect this is because of their limited lifespan (i.e. in service but the opened bottles also have a rather limited shelf life) and relatively high cost. Enter high-temperature vulcanizing (HTV) silicones and rubbers. On the first glance, this looks unreasonable. Vulcanizers start in the higher three figure range (Euro that is). On a second glance, vulcanization is not rocket science. Delivering heat in the 150-200 degree C range evenly is something we all need in an ordinary household oven, otherwise our cakes would turn out quite bad. Pressure can be supplied by clamps. This is not a hack I made up but something that has been proven in practise and even HTV silicone manufacturers suggest this for DIY purposes. However, I would not advise to do this in your household oven as silicones can smell quite badly and are generally not food-save.
Unfortunately finding advanced information online can be somewhat difficult. Good starting points are this video by Tom Mason and the rather small but incredibly worthwhile YT channel of Making Miniatures. Beyond that there is not much quality content on YT. (Semi-)Professional jewellers are our best friends here as this is the prime audience these silicones are targeted at and you find most advanced information on forums dedicated to making jewelry. You will quickly find that the gold standard silicone manufacturer seems to be a company called Castaldo – we are interested in their Econosil branded silicone as this can withstand higher temperatures (incidentally the same material Tom Mason uses – I discovered his video after I made my purchase). The first real challenge is to acquire said silicone. If you are outside the US or UK, this may become somewhat frustrating. While I found a local supplier, their prices were a bit high for my standards. Then I noticed that the jeweller’s community in Eastern Europe seems to be way more healthy and alive with the result that I found several Polish and Czech companies selling Econosil. After many emails, partly machine-translated, I found a very friendly Polish dealer willing to send one package (2.25 kg) to Germany, at almost half the cost of the previously found German-based listing, including express shipping! The package arrived within 3 days. So if you live in the EU, highly recommended to check sellers in other EU countries!
As for dedicated equipment: I bought a toaster oven, several tools (which also may come in handy for other DIY projects, so I don’t count them), a solder bath and a laddle made for casting lead bullets I believe. So overall, this seems to be in a similar price range to casting resin.
Having acquired all the raw materials, I will discuss how to make a mould frame in the next post.