Purses Part 9: Time For Metal!

Last time you saw the molds for making wax replicas of the purse pieces. Well the next obvious step is to turn those wax replicas into metal.

I cast metal (bronze, sterling silver, and pewter) on a fairly regular basis. Bronze and Sterling are what I think of as “hot” metals – they require temperatures of over 1700 degrees Fahrenheit in order to melt and become liquid. Pewter, on the other hand can be melted on a camp stove (500 to 600 degrees depending on the alloy).

The technique that I use for casting most of my “hot” metal is called Lost Wax Casting. A basic summary of how this works is that the waxes are anchored into a stainless steel flask, a plaster like substance, called investment, is poured into the flask and allowed to harden. The flask is then turned upside down and heated. The wax flows out, and in the later stages of heating (over 700 degrees), burns away completely. The investment is now the mold into which the molten metal will be poured. The image below shows the basic layout of the stainless steel flask, wax and investment. This flask is ready for the molten metal to be poured in.

Lost Wax Casting Flask

 

 

 

 

 

 

 

 

So, I put my waxes into flasks, invested, heated, and poured my metal. And the result? This picture shows the original artifact, and the newly cast, and cleaned up, bronze replicas.metal purse pieces

So what happens now? Well, I spent a bit of time filing and fitting the pieces together, and removing any rough spots. I wanted the pivot to spin easily, just like the original artifact does.

Once I had the pieces fitting together well, I needed to measure exactly how long the pin on the bottom of the pivot needed to be. If I cut it too short there will not be enough metal to peen over to hold the frame together, and if I cut it too long the fit of the frame will be super loose, and probably bend when I try to rivet the end. The fit on all of the period frames that I have seen is always fairly snug. So I marked the pin with a magic marker with the washer in place. This picture shows the marked pin with the washer off. I couldn’t find a smaller tipped marker (the Studio elves must have borrowed it again), so I knew that I needed to make the cut about half way across the ink mark.

purse frame pivot marked

I cut off the bottom of the pivot pin, smoothed the end, made sure that the end was at a right angle to the pivot pin, and reassembled the purse frame. The assembled purse frame was then put into a machinists’ vice and the end of the pivot pin was peened over with a hammer. And here is a picture of the result!

Riveted purse Frame

Next Time: Time for Purse Frame Rings

Purses Part 8: Where Do We Go From Here?

I realized after I posted the last blog that some folks might not have a clue about the process of riveting. Riveting was one of the most common methods for joining base metals together prior to the advent of modern soldering techniques and fancy gas torches. If you are interested in reading about modern soldering techniques. I wrote a blog on the technique a while ago.

But back to riveting. I made a quick, and not particularly artistic, picture of the basic riveting process. How is that for a fancy hammer?! But hopefully this gives you the basic idea. The metal of the rivet, or the end of the purse frame bar or pivot is simply moved by hammering.

Riveting

But back to my process! I also spent a ton of time looking at examples in museums. I found several at the Museum of London that had a similarly shaped purse bar and pivot. This purse frame was photographed upside down, but you can see that it is very similar. And this purse frame is not only similar, but also has a surviving purse frame ring. Excellent! Now I even have a potential model for the ring on my purse frame!

Next it was time to actually make a mold of the frame that I have. I used modern materials to make my molds. Because the actual artifact is metal I was able to use silicone mold sheets to make the initial mold. This material requires heating, in a special press known as a Vulcanizer, to create a rubber-like mold. Once this mold was created I was able to remove the original artifact and inject molten casting wax into the cavity of the mold. This wax creates an exact replica of the original artifact. I made several copies of the original purse frame in wax, and then began cutting the wax apart into the individual pieces that make up the purse. At this point it was possible for me to repair any flaws in the original purse frame pieces, like corrosion or other pitting. Once the individual pieces of the purse looked the way I wanted them to, I was able to use another modern silicone mold material, called Room Temperature Vulcanizing Silicone (RTV), that allowed me to easily create a mold of the individual wax replicas of the purse pieces.

Purse mold and waxes

Here is a picture of the original artifact and half of the Silicone mold that I made from it. At the bottom of the picture are the three RTV molds that were made of the individual repaired waxes. The new waxes that can be cast from these molds are the red objects above the RTV molds. You can see that I extended the worn and peaned ends of the original purse bar so that they would be long enough to hold new purse bar rings and still have room to be peaned over. I also extended the central pin on the pivot of the purse so that it will be long enough to go through the purse bar, put on the washer (shown on the right) and still have room to be peaned over.

Next Time: Time For Metal!

 

Purses Part 7: Back Down to Earth

Having looked at some of the truly amazing purse frames that were available as luxury goods in the Late Middle Ages in Europe, it is now time to come back down to earth and my original project to study and create replicas of original purse frames.

So, this is what I decided to start with.

My Purse frame with words

This is a picture of the actual artifact that I own. I have broken pieces of several purse frames, most of which are for considerably larger purses, but I decided to start small and simple. My goal with this purse was to replicate the actual frame of a real purse, without any of the preconceived notions or gaps in knowledge that I had on my last project. I also wanted to see if I could actually cast all of the pieces that they would have cast, instead of using a bunch of formed metal pieces. I wanted to create a purse frame that any middle class individual from western Europe would instantly recognize as a “normal” purse frame.

First let’s give a few facts about my purse frame. The frame was found by a metal detectorist in England. It is cast of bronze. The purse bar is 61 mm long (2 3/8 inches) and the pivot top is 13 mm across (about half an inch) and 22mm top to bottom (about 7/8 of an inch). It is a small purse, probably originally intended for coins. The pivot actually does spin around all the way on this purse frame. I am not certain what the advantage to this would be, but perhaps turning it with the front against you would make it more difficult for pick pockets to get into.

So how did I start on this project? First I spent quite a bit of time just looking at the frame. I wanted to understand how it was made.

Was it all cast? Yes, although it is possible that the washer at the bottom of the pivot was actually created from a heavy piece of plate bronze.

Were there any places that were soldered? How were the pieces held together? The answer to both of these questions is related. There is no detectable solder on the piece. The parts are all riveted together by peaning over the ends of the metal purse pieces.

How many pieces were there? What pieces appear to be missing? This is a difficult set of questions to answer. The surviving frame consists of three pieces: the purse bar, the pivot, and a washer on the bottom of the purse bar that helps keep the pivot in place while allowing the pivot to rotate. The bare ends of the purse bar show wear marks. There was originally at least one purse ring, and possibly two. There does not appear to have been a washer on the ends of the purse bar to help retain the purse frame rings, but it is possible that there was, and it didn’t leave a discernible mark.

Next Time: Where Do We Go From Here?