Time: December 2009
Purpose: To build a furnace cheaply in a matter of weeks which is capable of casting a silver ring for a girl as a Christmas present.
Background Information:
When I took this project upon myself, it was around December of 2009, around the middle of my sophomore year of high school. I (formerly) had my eye on a certain girl that year, and I was thinking of getting a present for her for Christmas. However, looking through Target, sorting through various little knick-knacks which had been mass-produced in Chinese factories, which had been placed there for the sole purpose of being purchased by various Americans in the hassle of the holiday season, I simply could not find something that I actually wanted to get her. Most of the things which I saw most likely were destined to later fall apart because of their poor design and construction. Upon a stroke of inspiration I decided that I, being skilled in the ways of Chemistry, would take it upon myself to build a furnace from the ground up and make her a ring of silver. I couldn’t think of a more honorable thing to do, being that not most people cannot say that they received or even given a gift that was created by placing it into a fire, melting it, and then pouring it into a mold by hand.
Procedure:
Wax Models:
1. Carve object(s), or namely ring, from wax to use in lost-wax replacement mold.
2. Acquire food cans, being sure that the tops are removed and the bottoms are intact.
3. After carving, place models in plaster molds, leaving enough space for objects to burn out. When mixing plaster, be sure that the consistency is more like paste rather than soup, as otherwise it will be difficult to accurately create the molds. Then, set aside and allow them to dry.
4. Burn out wax from molds to allow the correct space for the molten metal to flow into.
Furnace
1. Acquire large metal garbage can designed for exterior conditions, two coffee cans (or larger types if desired), several food cans, and a thick metal grate.
2. Fill bottom of can with dirt to the height which the air duct is desired, and then place first coffee can upon the dirt inside of the garbage can, with the open end up. Create a hole in the side of the garbage can which is large enough for the food cans to fit through. A propane torch should enable this job as painless, as the metal becomes very pliable upon application.
3. Connect the food cans together, which should create a large pipe that runs through the side of the garbage can. Try to angle the pipe downward outside of the garbage can, in order to prevent the billows from overheating. Duct tape is an option.
4. Connect the food can pipe to the coffee can inside of the garbage can, so that when air flows through the pipe, it can enter into the coffee can, and later into the fire. Duct tape is an option.
5. After securing the pipe to the coffee can, pour in more dirt around the coffee can and pipe until the entire contraption is covered, with the level of the dirt being equal to that of the open top of the can.
6. Place thick metal grate over dirt and can opening.
7. Retrieve the second coffee can, and create several small holes throughout the bottom of it. These will allow the air to flow into the fire, thus rapidly increasing the speed of oxidation.
8. Place second can directly over the first can, with the open end facing up as done before.
9. After this, begin to add more dirt around the second coffee can, continuing to pile it until it completely surrounds the outside of it.
10. Once this is completed, allow moist soil to dry, and the furnace is completed. It should be noted that clay soil was used for this project, although it is assumed that any type of soil should work.
Casting
1. Acquire silver (1 oz. coin was used). Silver is often available in pawn shops.
2. Acquire a crucible, which should be purchased online if no specialty shop is available. During this project several attempts were made at creating makeshift crucibles, but none have succeeded thus far. Crucible tongs are also helpful.
3. Start charcoals in a charcoal starter, or simply light them in the furnace with a propane torch. Lump charcoal should be used. After hot coals are in the furnace, being placed in the top coffee can, use a long set of tongs to place the crucible with the silver into the midst of the furnace, being sure that the sides are surrounded by coals.
4. WARNING: Several safety precautions are recommended throughout this process. This includes
-Thick Leather Gloves
-Safety Goggles
-Leather Clothing
-Close Toed Shoes/Leather Boots
-Long Sleeves and Pants That Reach the Ankles
-Good Tongs That Can Securely Grip the Crucible
-Sunglasses if Necessary
If one follows these safety precautions the likelihood of an accident at the hands of the furnace becomes significantly reduced. Liquid metal is very dangerous, and will flare up if water falls into it such as rain or snow. Its temperature is more than hot enough to instantaneously destroy any part of the body that could come into contact with it, so one should never handle a crucible directly with the hands, even if they are wearing leather gloves.
As one uses tongs to handle the crucible, one must be sure that the tongs do not constantly sit inside the fire, as this will cause immense heat to travel up the metal body of the tongs, and if the tongs have any sort of rubberized handle, these may begin to melt. It is important to be sure to have some water or snow nearby that may serve to quickly cool the tongs should the heat become too severe for the leather gloves. Also, liquid metal can be very bright. While sunglasses are one of the less important safety measures, they are handy to have in case the eyes have difficulty looking at the fire. It should also be noted that the strength of the brightness varies from metal type to metal type. While some may be observed freely, others could potentially cause blindness. As a precaution, one should always check with good sunglasses first to see whether or not it will be safe to view with the eyes alone.
5. As coals are burned up, replace them with new ones. Allow the coals to burn
for about 10 minutes without any extra air being blown into the air pipe. This
will allow the crucible to warm up slowly, which will prevent it from
cracking.
6. After allowing the coals to burn naturally for ten minutes, plug in an ordinary hair dryer to an electric power source, and place the barrel end of it into the air pipe. This will serve as the bellows. Turn it onto the low setting and allow it to burn for another 10 ten minutes, replacing coals around the crucible as necessary.
7. After waiting for another ten minutes on the low setting, change the blow dryer to the high setting, and repeat ten minutes as before. The silver should melt at this point after enough time.
8. Check to see if the silver is melted, and do not pour until it is completely liquefied. While waiting the mold should be already prepared and close by.
9. Once the silver is liquefied, one should use the tongs to grab the crucible and pour the metal into the mold. This should be done quickly and carefully, as it may resolidify if one waits too long. Remember that the liquid metal is almost 2000˚F[1], and will quite easily burn through most objects if spilled.
10. After pouring the silver, place the crucible in a safe place, such as a container with plaster inside, in which the crucible can gradually cool down in the same manner as it was heated up. If the crucible is cooled too rapidly, the thermal shock could cause it to crack, which would be highly dangerous if any liquid metal was still left inside.
11. The silver in the mold should cool very quickly, and after about 5 minutes or so it should be ready to touch, although one should not use fingers to do the first test. If it has cooled, then the object should be ready to be pulled out from the plaster, cleaned, and polished, although little polishing should be necessary.
12. After casting, allow the furnace to continue burning, but do not add any more fuel. Once most of the charcoal in the furnace is gone, turn off and put away the blow dryer, and simply allow the rest of the coals to die down naturally.
Pre-Project Research Data:
This is a compilation of the information that I gathered from various books and sources on the net in preparation for this project.
Chart [1]: Melting Points of Various Metals in Fahrenheit and Celsius Scale Degrees
| Metal Name (Symbol) | Melting Point (˚F) | Melting Point (˚C) |
| Aluminum (Al) | 1220.58 | 660.25 |
| Zinc (Zn) | 788 | 420 |
| Copper (Cu) | 1983.2 | 1084 |
| Nickel (Ni) | 2651 | 1455 |
| Iron (Fe) | 2800 | 1538 |
| Chromium (Cr) | 3464 | 1907 |
| Vanadium (V) | 3470 | 1910 |
| Titanium (Ti) | 3034 | 1668 |
| Silver (Ag) | 1763.2 | 961.78 |
| Gold (Au) | 1947.52 | 1064.18 |
| Tin (Sn) | 449.4 | 231.9 |
| Lead (Pb)* | 621.5 | 327.5 |
*Lead was not originally included in my charts, but has been added for the benefit of the reader.
Chart [2]: Various Metal Alloys with their Percent Composition and Usage
| Alloy | Composition | Usage |
| Sterling Silver | Ag 92.5% Cu 7.5% | Silverware, jewelry, etc. Used for its strength. |
| Attempted Project Alloy* | Ag 97.0% Cu 2.9% Au 0.1% | Ring Project. Tried to create a strong alloy resistant to corrosion and tarnishing. |
| Cast Iron | Fe 96% C 4% | Cheap strong material for construction, etc. |
| Stainless Steel | Fe 80.6% Cr 18.0% C 0.4% Ni 1.0% | Knives, boats, construction, etc, for its resistance to corrosion. |
| Spring Steel | Fe 98.6% Cr 1.0% C 0.4% | Springs, for its durability. |
| Surgical Steel | Fe 67% Cr 18% Ni 12% Mo 3% | Knives, scalpels, surgical instruments, etc, for its resistance to rust, its sharpness, and reliability. |
| Bronze | Cu 87.5% Sn 12.5% P Trace amounts | Weapons, statues, for its historicity and beauty. |
| Bell Metal Bronze | Cu 75-80% Sn 20-25% | Used for bell making because of its tonal qualities. |
| Brass (Dutch Metal) | Cu 80% Zn 20% | Used as a gold replacement in cheap jewelry. |
*While this was initially the alloy I intended to create, I do not think I succeeded. After casting I noticed that the piece of copper which I had put into the crucible was still stuck inside the extra silver from the crucible, meaning that it had not mixed with the rest of the metal. Thus, it is very likely that the ring was actually composed of 100% silver.
Design [D1]: The Furnace
Diagram [D2]: Making the Mold
Diagram [D3]: Preparing Mold*
*During project mold was not actually baked, but has been included for the
readers' benefit.
Diagram [D4]: Casting*
*During the project, coals were not used to warm mold. They would be helpful in reducing the thermal shock of the silver, thus producing a better cast.
Project Overview:
Pre-project:
Learning exactly how to even go about doing this took quite a bit of thought. Most people do not know how to make things anymore. Most things nowadays are created in factories, far away from the civilian eyes and the public mind. After some research, I discovered that the melting point of silver was almost 2000˚F [1], much higher than any fire I had ever created before. I wasn’t even sure how I could make a mold. Most substances I could think of would most likely not be able to withstand that kind of heat for any amount of time, let alone be able to create an acceptable shape for it to form in.
However, being determined to succeed, I continued to search. I figured that if ancient peoples with less equipment and technology than the world of today were able to produce beautiful articles from metal and wood, I figured that today, I too could form silver in a mold.
As far as the method to use for casting my ring, I discovered in a book somewhere that ancient silversmiths used a method known as the lost wax replacement method (See Diagrams [D2], [D3] and [D4]). This seemed to be a good option as wax is cheap and very easy to work, and would be much more yielding in its creation than a wooden model would.
After creating the wax models for the objects which I wished to create, I then proceeded to build the furnace, using an idea that I found online in which a person who casts silver decided to share (See Design [D1]).
After the furnace and models were complete, the molds had to be made. This was by far the least enjoyable part of the process, as being inexperienced with plaster the molds were very difficult to create. I had originally intended to make several objects besides the ring, but only the ring turned out to be usable. I did succeed in submerging a wax Packers’ logo into plaster, but due to the nature of how large it was I was unable to burn out the wax from it, thus making the mold unsuitable to use. Also, due to the amount of water which I used for the plaster, the wax models floated in the plaster rather than sank, which distorted my original plans, and made it very difficult to simulate the models.
Casting:
Before the night in which I cast the ring, I had performed a series of tests using less valuable metals, such as copper and aluminum. During these tests, I had not yet acquired my crucible. Indeed, I had been hoping to use simple clay dishes as the crucible, in which I attempted to melt a number of old and new pennies in an attempt to make brass. These makeshift “crucibles” cracked almost instantly and caused me to lose my pennies. It should also be noted that the new pennies, being made of zinc, did not melt as I had intended them to. Instead, the zinc inside of the pennies began to spontaneously combust in a show of dazzling bright green, very similar to the way in which magnesium burns when it is heated. Thus, clay crucibles were out of the question.
In an attempt to melt a large section of copper pipe, I attempted to use a stainless steel mixing bowl in order to do the job. The problem here that I soon discovered, however, was that if the “crucible” was not completely submerged inside of the coals, the copper could not get hot enough to liquefy. By turning the bowl onto its side I succeeded in making the piping glow significantly brighter than previously, however they still did not melt. At a loss for hope, I simply took some tongs and thrust the entire mass of copper directly into the fire, not contained in any container whatsoever. This achieved results. In a matter of seconds (less than a minute), the copper glowed brighter then ever before, and I could see it physically begin to melt. I then retrieved as much of the pipe as I could, but the metal was now so soft that some parts became lost in the fire. I had not yet completely liquefied anything yet, but it was then that I realized that the metal must be in contact with the flames if the heat of the furnace was to be utilized enough to melt it.
Thus, knowing that the bowl was too large, I attempted to use food cans to melt aluminum cans. This was interesting. I could see the cans melting very quickly, turning a bright orange very much like the copper had before them, as it was in the pliable stage. However, the moment in which the aluminum melted something happened which I had somewhat feared subconsciously but had not really expected. The aluminum transformed into a searing, eye-bleeding, bright white, and then it burned straight through the bottom of the can, even as I had been lifting it to examine it. The intensity of the light is difficult to describe. The only way that I can find the words to even attempt to explain it is that it was very scary, and it was brighter than the light which magnesium creates as it is burned. I am not sure if aluminum always behaves this way, as I have little experience with it, but this time it certainly did. I would never have guessed that such a common metal could become so frightening when it is liquefied.
As the food cans were tested, they all disintegrated without fail. I even attempted using two at once in order to increase its stability, but this did little to remedy the problem, have little to none effect upon it. Thus, I then realized that most materials were not crucible grade, and I would actually have to purchase a crucible. I did this, on a site titled www.silversupplies.com, the quality of which I was very pleased with. The shipping was expensive only because I was running out of time before Christmas at this point and desired the most expensive shipping possible. For the readers’ purposes, this most likely will not be the case, and the crucible itself only cost me $15. Perhaps a future project could be dedicated to constructing a crucible similar to the one I purchased there, however that is for a later time.
Having the crucible and the mold ready, I now needed to repair the furnace. After testing it for so many times, the 2nd coffee can (the furnace chamber) had all but completely disintegrated, much in the same manner in which the food cans which I had tried to melt aluminum in had done as well. After replacing the furnace chamber and cleaning the air duct (see design [D1]), I was ready to melt the silver. This process went smoothly and went just as recorded in the “Casting” section of the procedure, with the exception being that there may have been some variation which differed in step #12.
I hope that this report has been both helpful and informative, and that the art of metallurgy becomes more exact throughout the years. Comments, corrections, additions, and suggestions are always welcome.
--Brett Benischek, the Benischek Lab
Click here to see the photos from this project.
Click here to download a pdf version of this report.
