We have begun to disassemble the furnace to see if we can determine what happened and what we need to do to correct the problem. So far, we have removed masonry down to the tap hole and sectioned the tap hole itself.

Over the next few weeks, we will be getting further into the furnace structure to see what else might be revealed and to figure out how to remove the 500-pound mass of bronze that remains in there.

We have not yet removed the molds from the ground—something we will have to do to prepare for the next pour. The molds were almost certainly damaged by an afternoon downpour the day of the pour, and we are not going to re-use them.

The founders are in the process of making a whole new set of molds while the weather remains good this fall. Much of this is an outdoor activity, and we want them to be complete and ready to use when we are set to make another attempt early next spring.

Over the winter, with new information in hand, the masons and founders will determine what modifications should be made to the furnace to increase its heating capability and any other problems associated with it. They will rebuild/modify the furnace next spring when weather and time permit, and another pour will follow shortly.

We started heating the furnace on Tuesday morning and buried the mold next to the furnace late Tuesday afternoon. We kept the heat low to bring up the temperature slowly until about midnight. At that point, we ramped up the heat until it was going strong on Wednesday morning.

Because the quantity of bronze was so much greater than in previous pours, we did not know exactly when to expect the charge to melt. By mid-afternoon, it was taking longer than anticipated, so we increased the airflow through the furnace using a fan.

To all appearances, it was burning well, and by about 4:30, the bronze appeared to be liquid. The crew then punched the plug out of the taphole. Aside from a few dribbles, nothing happened. Repeated tries were made from both the outside of the taphole and probing at the opening from inside, to no avail. A few minutes later, the skies opened up and it poured rain. We were all a pretty dejected and sad-looking crew.

We will not know what caused the failure until we partially disassemble the furnace. We need to do so to remove the 550+ pounds of bronze inside, and it will allow us to closely examine the masonry and metal.

In the meantime, our best guess is that, though undetected, there was a lump of unmelted bronze that was swept almost immediately into a blocking position. We are taking a few days to recuperate and grieve. We’ll post more when we have it.

Watch video from the first test pour.

Watch video from the second test pour.

The light-three will require us to melt approximately 650 pounds of bronze. The mold is in three parts: one for the barrel without its breech end (cascabel), one for the cascabel, and one for a large “dead head,” the mass of bronze above the barrel portion of the casting. The overall length of the assembled mold is 67 inches.

In the process of further machining the coehorn, the small mortar used to test the process, it became evident that the casting had a large area of porosity near the muzzle. It is large and deep enough to render the casting unusable. The flaw probably was due to the problems explained in the March 9 post. Despite the lack of a definite explanation for the problem, we have decided to move ahead with pouring the light-three barrel. It will have its own casting characteristics, and there is little to be gained by additional smaller pourings.

If anyone is interested in coming to watch the pour, you are welcome to join us at the furnace adjacent to Great Hopes Plantation opposite the Colonial Williamsburg Visitor Center. We need all the crossed fingers we can get. Bring a chair and water, wear a hat, and remember that the nearest restrooms are at the Visitor Center, a few minutes’ walk from the furnace site.

Plan your visit to Colonial Williamsburg.

Learn more about the cannon project.

We have cleaned up the exterior surface of the second coehorn casting, and it is much improved over the first one. The porosity and shrinkage problems are much less, diminishing toward the lower part of the casting. So far, it does not appear they are serious enough to prevent the casting from being machined into a workable barrel.

The larger problem this time, somewhat to our disgust, is inclusion of what appears to be refractory mortar near the outside of the casting, especially around the moldings. This probably happened with the first casting as well, but there were so many inclusions that we didn’t focus on it as one of our primary concerns. We believe the mortar material was knocked loose when we rammed the crook into the tap hole.

We’re now looking at the construction of the tap hole, and more promisingly, a gentler and more controlled way to knock the plug loose. Despite these problems, we have decided to go for broke and proceed with casting the light three when weather permits this coming spring.

The toolmaker is about to return to boring the coehorn so that we have full information on its porosity. The founders are making the strickle for the light-three so that they can begin to make the pattern and mold when the weather allows them to set up outside again. The masons are checking the furnace after our recent snows to make sure it is ready to go. When we have set a pour date, we will post it.

In the meantime, the wheelwrights and blacksmiths are moving ahead on the limber construction, with the hope that it will be done within four or five months. We are tackling the limber before the cannon carriage because we need the exact dimensions of the finished barrel trunnions in order to forge the carriage ironwork which receives and secures the barrel. The carriage is best tackled only after we have a barrel in hand.