How To Cast An Ingot
Casting an Ingot of Fine Silver
An expansive tutorial which walks through the process of casting various forms of metal into a work-able ingot form. Written by a professional metalsmith, features techniques and tips from years of experience. Includes material list, references, and complete explanations.
Casting an ingot of metal might seem simple enough of a process, 1) grab some metal, 2) apply heat and 3) dump it into an appropriate vessel, but it really does require a certain level of care and knowledge to do it properly. Continue reading for the full process walk-through.
What you need to cast an ingot
-Some sort of precious metal preferably gold and/or silver
-Tinted Safety Goggles
-Fuel Tank and Regulator
-Oxygen Tank and Regulator
-Tweezers/ metal tongs
-Water (preferably in glass or metal container with a wide opening/ top)
-Oil/ soot (or some other “lubricant” if your ingot mold requires it)
-Brush (size will depend on the size of the ingot mold)
1. Materials, Fuel Regulators, & Prep Work
The first thing you need to take into consideration is what material you will be casting. Not all metals behave the same way and all of them have very particular characteristics that need to be taken into account before we can begin (melting temperature, purity, compatibility and this barley scratches the surface).
In this particular case, I am going to talk about fine silver, fine silver is as close as we (humans) can get to pure silver. It is 99.99...% pure silver. It is very soft, works very easily, is rather forgiving (as far as metal goes) and does not tarnish much.
Considering, we know that silver melts at a fairly low temperature (1763F) we need to have our tank regulators set accordingly. Yes, we do want to melt the material but we don't want to overheat it and "cook" it by being too aggressive. It is actually possible to "boil" off some of your metal if you attack it with too intense of a flame, causing it to literally evaporate in the form of bright sparks. When working with precious metals, you want to use a flame that is big and hot but not super intense and heavily oxidizing you want is to be almost a little reducing and a little "bushy" (not a super fine tip on the flame). To achieve this, I usually have my propane fuel regulator set to around 5psi and my oxygen regulator set to no higher than 10psi (typically I work between 5psi and 10psi sometimes lower, a little pressure goes a long way)."
2. Quantity of Materials & Prepping Notes
The next step is to decide how much material you will be casting. Not very important when creating an ingot that will be processed into other forms but, sometimes a very crucial step; for example if one was preparing a "charge" for a lost wax casting/ mold, where you need a very specific amount of material to fill a void. Another example which comes into play in my work is; I like to cast ingots into one or two ounce ingots simply so I can easily keep track of how much material I am using/ processing.
Important: Make sure your work space is rather flat and constructed of appropriate materials; if your ingot mold is not flat enough your material will pool on one side (the high side) and possibly spill over causing a mess and a waste; alternatively your material could flow to the other side (the low side) and be stretched thin (these issues are most concerning when casting a wire ingot like I will be doing here but may also be relevant with other molds).
Note: It is also important to know what type of mold you have and how it works. Many times molten metal will stick to other metals so many molds need to be lubricated to provide a barrier that will keep the two metals from sticking together. I usually dab a little motor oil over my molds with an old brush before I cast into it.
Safety Notes: Always use a torch and hot molds in appropriate surfaces and work areas. Many people choose to do this process using gloves and special safety glasses, protecting your body is always a good idea. I find that gloves interfere in my case more than they help; so I take extra care around hot working areas and always have a pair of Kevlar gloves within reach just in case. Same with eye wear; sometimes it helps, sometimes it gets in my way. For this reason, I like goggles that have a flip screen so you can protect your eyes when you want to, but still easily be able to see in the daylight again.
3. Pre-heating - Very Important!
Now it's time to get cooking. Lubricate your ingot mold, spark up your torch and begin to pre heat your ingot mold and crucible. This is a very crucial step because it allows the surface of the ingot mold and crucible to become hot and ready to accept the material; as well as not having to subject the material to excessive heat before the crucible is at an appropriate temperature.
Very Important!: If you don't pre-heat your ingot mold your material will get shocked into a small tightly packed crystalline lattice structure and probably be weak, fragile, brittle and prone to cracks, inclusions and bubbles
Pre-heat your crucible as well, the hotter things are the better, you should be sweating a bit or you're not doing it right.
Note: Please notice the color of the flame in your crucible, particularly look for a greenish color; if you have ever cast copper in a foundry, this green hue is a telltale sign of a nice reducing environment. This environment is crucial in keeping the copper from oxidizing with the air especially in an intense fire which needs oxygen to burn. Keep heating your crucible until it is glowing a bright orange/ red, then you're ready to add your material.
Note: If we were to prepare an alloy, say of sterling silver or a gold alloy, the general rule that I follow is to start with whichever material has the highest melting point, and proceed to gradually add the other metal/s in small quantities; again starting with whichever material has the higher melting point. For example: Let's say we were making a hard 12K gold of 25% copper, 25% silver and 50% gold. We would first melt the copper (1981F) then add small amounts of gold (1945F) and finish by adding small amounts of silver (1761F) until the full amount of material has been added and melted; if done properly and agitated well the mixture should be consistent and molten throughout. Also, note that it is not uncommon for metal smiths to cast an ingot of an alloy two or three times to ensure it has a consistent distribution and color. Now with our material in our nice warm crucible we can begin to heat and melt the material.
4. Melting the Materials
--You will begin to see the material begin to glow a bright orange/ red just like the crucible and it may become difficult to see what is actually happening inside the crucible. A pair of specially tinted goggles or safety glasses may be helpful if you want to protect your eyes and see the action.
Note: If you see sparks coming out of your crucible your fire is to intense and you should pull back your torch, add more fuel or decrease the oxygen. You want your metal to gradually melt as uniformly as possible.
5. Purify & "Jiggle Test"
Now, we need to purify our metal and make sure its's completely molten.
Once you see a very reflective/shiny molten silver bead like blob at the bottom of the crucible you are getting very close. Now would be a good time to add a sprinkling/ dash of flux into the crucible to purify the material of any undesired contaminants. To do this, simply remove the torch for a moment, and sprinkle the flux into the crucible (watch your fingers as everything should be very hot by now).
To do this, I will typically use a test I call the "jiggle test"; agitate the crucible by jiggling the handle a bit. If you see the material swirling around the crucible very freely and bouncing and jiggling with surface tension and ripples (like water in a glass) you should be good to go. *Tip: It can be helpful to prod into the bottom of the crucible with a steel rod (or clothes hanger) to check for possible clumps of not quite molten material, this should be done very quickly to avoid melting the rod into the alloy. As soon as you are certain all the material is molten you may proceed to casting.
Finally, it's time for the climactic, sometimes intimidating, part of the process; pouring this precious molten material you have just been sweating over and making sure that you don't miss!
The most important thing to keep in mind is that you want the metal to reach the mold completely molten and to stay molten in the mold until it begins to solidify (you don't want it to start solidifying while you are pouring).
To help transition the material from one vessel to the next, keep your flame on the edge of the crucible on the side you will be pouring from. Position your flame on the edge of the crucible, also heating the mold. (I pour to the left, holding the crucible in my right hand and the torch with my left hand).
Once the flame is in the correct position you can begin to tip the crucible over to the side and the blob of metal should move easily into the corner. Begin to tip the crucible onto its side allowing the material to flow up the side and down into the mold. You want the edge of the crucible to be exactly above where you want the material to fall or flow into. Begin to pour into one side of the mold and allow the material to flow at a constant smooth rate and fill the cavity toward the other end.
Note: It can be very useful to prepare several things to be cast at one time so that you can take advantage of your nice warm mold and crucible. Allow your ingot to cool down a bit and solidify, if your fast and good enough you should be able to watch your metal solidify and see the crystal lattice structures forming over the surface of the ingot.
Once things have cooled down a bit and your ingot stops glowing you should be able to turn your mold on its side and have your ingot plop right out. Allow your ingot to cool slowly to ensure that all of the crystal structures have time to form large strong organized patterns. This is a crucial step for some materials that cannot handle rapid cooling (quenching) but is a good idea for all materials (unless you are trying to achieve something specific) as we always want our material to be strong and well formed.
Once it has cooled properly the ingot should be placed into a warm "pickle" bath to remove any unwanted residues and pieces of flux that may have poured out of the crucible with your material.
9. Clean, Dry, and Done
After pickling, it is a good idea to rinse off the ingot in clean water and dry it off with a clean rag or paper towel (preferably a rag that you can wash and re-use). And once your ingot is clean and dry, it's ready to go.