Forge: Backstory

The forge project is nearing completion, but first I think I should update you on what has already happened.

The project started after I started making charcoal (I do not plan on writing about this here, but when my book is finished, I will provide a link to the information) was a coal forge. The forge was one of the things on my list of projects to include in the book, so I started researching materials that can withstand the heat produced. I quickly discovered that I needed to build the forge with a hole in the bottom, to pump air up through the charcoal. I already knew that clays and ceramics were probably my best bet for withstanding high temperatures, but I also knew that even clays can crack if heated quickly. So I begun my research into fire brick and fire clays, but at the same time I bought a 6in clay flower pot at a local hardware store.

The clay pot seemed like an ideal forge, because it already has a hole in the center of the bottom. The one thing I was worried about was cracking. To put air into the hole, I bought a copper pipe reducer and used my Dremel to cut the larger end into quarters, which I bent down and drilled holes in, so that I could screw it onto the bottom of the pot.

The drilling of the pot, with a masonry bit, worked fine, except that the holes did not quite come out straight. This did not seem like a problem until I was tightening the machine screws down and the stress created by the screws being in holes that were not quite straight caused the pot to crack across two of the holes. At this point, I knew the cracks would expand as the pot heated, but since I had nothing to loose (the pot was essentially already ruined), I decided to fire it up.

I had also bought a small fireplace bellows when I got the pot and the pipes (I also bought a few pipe fittings and a length of pipe, to direct the air into the fitting on the bottom of the pot). So I put some of my charcoal (made from fir) into the pot, used a lighter to get it smoldering, and piled in more, until the pot was full of charcoal. Next, I connected the bellows to the end of the pipe contraption (the end fit perfectly into a 1/2in coupler) and started pumping.

I quickly discovered that the small bellows was not sufficient for the task. Besides that, one of the tacks used to hold the leather on was too close to a moving part and stated wearing a hole in the leather. I returned the bellows to the store, since it was faulty, but I did not buy another one, because it did not provide sufficient air flow. As such, I am going to have to provide instructions on how to make a large bellows in my book, otherwise the forge will be useless. (I may post that project here, when I get around to doing it.)

My solution to the air flow problem (since I do not have time to make a large bellows) was to go to Salvation Army and buy a few used blow dryers. After disassembling one, in an effort to take out the heating coils, I ended up with a blower that operates at 12v (this was not intentional, but it turns out that the heating coils were an integral part of the 120v power supply leading to the 12v motor and the motor will not operate at 120v without the coils). The other blow dryer had a "cool" switch, so I modified it to be permanently on the "cool" setting (it still generates some heat, but only a little). I also bought a fitting to reduce the blow dryer down to the size of the 1/2in copper pipe that I am using for air (I also had to use a little duct tape).

Once the air flow issue was fixed, I piled in the charcoal again and fired up the blow dryer. Within about 3 seconds, every bit of the charcoal was burning and fire was shooting up about 1 foot out of the 6 inch clay pot. My brother, who was watching, backed up in surprise and awe. I just laughed, because that is about what I expected. The blow dryer worked very well, but I will still have to build a large bellows, because the blow dryer is limited by the length of the cord and the access to an electrical outlet.

So, once the forge was properly firing, the small cracks from assembly became very large and many other cracks started forming. Again, this is about what I expected. I only fired up that forge once more, at which time the cracks became large enough that it would probably fall apart with any further use.

I did some more research on refractory clay or cements and found that many hardware stores carry a sort of fireplace cement that is supposed to withstand high temperatures. So I went back to the local hardware store and discovered that they did carry a fireplace cement that is good up to 2100F. I bought another clay pot and was more careful about the drilling this time. As such, I managed to cause more damage than the last time, however it was not in the form of a crack running up the side of the pot, but rather, just a bit of the bottom broke out. I was able to repair this very well, with some of the fireplace cement.

Once the pipe fitting was installed, I lined the pot with about 1cm thick of the fireplace cement mixed with sand (about 1/3 to 1/2 sand). Once this set, I covered it with a thin layer of fireplace cement without sand. This one looked much more capable than the first, but the clay pot began to get hairline cracks the first time I used it. In addition to this, the fireplace cement (which was originally rough black) turned glossy white on the bottom and lower sides of the container. Since the cement is rated to 2100F, this tells me that the forge got hotter than that.

After a few more uses, the cracks became wider. So I used a hose clamp on the top rim of the pot to prevent the cracks from getting larger and I filled the cracks with more of the fireplace cement, in hopes that the heat will fuse the cracks closed. This is where I currently am on the clay pot forge. I have not fired it since patching the cracks, so I do not yet know if the patches will properly fuse and fix the forge.

Now I am working on making another forge, using fire clay (much higher temperature) and a paint can (1 gallon). There is only one pottery supply place near where I live, so I went there looking for fire clay. Turns out that they do not carry it (and were not even sure what it was), but they do carry high temperature clay. So I have decided to make my own fire clay. I bought a 50lb box of Klamath Buff clay. My research tells me that to make fire clay, I need to add to this 24%-34% alumina (aluminum oxide) and 50%-60% silica (silicon oxide). Obtaining these has been an issue, so I started doing research on how to make them.

Since it turned out that alumina is just aluminum oxide, I decided to use electrolysis to rapidly oxidize some aluminum cans (I have a 5 gallon paint bucket where this is occuring, as I type). The silica, as it turns out, is one of the most common compounds in the Earth's crust and can be easily obtained in the form of beach sand. Of course, it needs to be powdered, so I will probably end up bulding some sort of rock tumbler to tumble the sand in, until it turns to powder. The alumnia will be mixed with water when it is done (because the electrolysis takes place in water), so I will just boil it down until it is a sludge and then filter it and dry it.

Theroetcially, if I were to just powder aluminum and mix that with the clay, it would work for the alumnia, because it would quickly oxidize the first time the forge was fully fired, but I do not want to take any extra risks, so I am going to do this right.

In summary, I now have a temporary clay pot forge that is not likely to last more than 10 more firings, even with the repairs I did on it. I also have and am making the resources for another forge that will be made from homemade fire clay and contained within a 1 gallon paint can. I have managed to melt aluminum in the clay pot forge, using a 1 1/4in steel pipe cap for a crucible. Once the paint can forge is done, I will be drilling some holes in the crucible to make it easier to support over the forge and easier to pour.

Once I have a significant amount of alumina and silica, I will write again. For now, I am waiting.