Hst-Snd-Cstng-art - 8/15/15
"Sand Casting in History" by Lord Camlan Bayne Wallace.
This article was submitted to me by the author for inclusion in this set of files, called Stefan's Florilegium.
These files are available on the Internet at: http://www.florilegium.org
Copyright to the contents of this file remains with the author or translator.
While the author will likely give permission for this work to be reprinted in SCA type publications, please check with the author first or check for any permissions granted at the end of this file.
Mark S. Harris...AKA:..Stefan li Rous
stefan at florilegium.org
Sand Casting in History
by Lord Camlan Bayne Wallace
I had been working at the bench for twenty years as a professional Goldsmith when I stumbled up on the SCA and its multifaceted avenues of the Arts & Sciences. It was a banquet of knowledge and I took a chair and began to feast upon the epicurean delights with a hungry spirit. So much to feed the eyes and nourish the soul with real meat, bones and marrow. I was hungry and brazen with adventurous persistence and this reminded me of my desires to feed my glutinous curiosity.
Then I discovered sand casting. It opened a doorway unto a world of unrestrained artistic expression. It can be defined as a science, but it does require some artistry to deliver an elegantly beautiful product in the end.
Casting with sand and clay is loosely defined as sand casting. However if we take a closer look at the composition of the investment material we will have a better understanding of the casting process. I shall attempt to stay within the time frame of 600C.E. to 1600C.E. in this examination of the different investment compositions. So let us begin with the descendants of the Celts, which were using clay, with a large amount of sand, mixed with it. They were making impression molds and casting bronze into the void left by the master. They were hand forming the molds and didn't use a frame. They were not using the lost wax process.
So let's step further along this path and we encounter Theophilus Presbyter around 1100C.E. in his tome "On Divers Arts". He gives instructions for making molds using clay and doesn't give instructions for casting with sand. He does however give instructions about using iron rings and plates, as a frame that he lines with clay. So this could possibly be interpreted as a casting frame made of iron, but it is an impression mold used to make a circular ingot that is later formed into the bowl of a chalice. He also uses clay as the investment material for "Cire-Perdue" also known as the lost wax method.
When we travel further along the timeline of history we encounter Vannoccio Biringuccio in 1540C.E. and his published work of "De La Pirotechnia". He does use clay to make many different compositions for casting bronze. He adds wool clippings, cow hair, wood ash and recommends that the craftsman use whatever is needed for the clay to work properly. He also gives instructions for making "Green Sand" and is seen as the Father of the Foundry. However we should take a much closer look at the composition of the investment material known as Green Sand. His instructions for making it is to use "Yellow Tuff", which is a Geological term for a particular type of igneous rock found near Volcanoes. Also "sand" is another Geological term used to define a particle size of material not its composition. So his instructions for making the Green Sand is to use fine-grained Yellow Tuff or river gravel and combine it with young ram's ashes and finely sifted old flour. Then he uses urine or wine to moisten it which is the binder and holds the investment material together. It is referred to as Green Sand as compared to Dry Sand. So it is comparable to green wood and Biringuccio had written that it could be used damp *.
Then he gives instructions for making "Powders in which to Cast Bronze". He gives instructions for making a composition using many things in combination or by themselves. He lists gravel, tuff, washed river silt, tiles, glazed drainpipe, brick and lists several different kinds of ashes. He also bakes it in a furnace and pounded it to create finer material and uses a sieve to separate it and then grinds it even finer with a potters color mill. He dries it out then uses "Magistery of Salt Water". Which is water saturated with salt to make it moist. And he uses a casting frame to form the impression molds in. He lets it dry and explained that it was a very tough mold and he could successfully cast bronze three of four times using the same mold. So finely ground materials bound together with salt was used in a casting frame during the Renaissance Period to cast bronze and other metals.
This does bring to light an entirely different approach to casting then I've seen taught or seen practiced by people at SCA events. I have attended classes where an oil sand known as "Pro-Craft" or "Petrobond" was being used and it's mainly composed of Silicon Dioxide, so it's not the same as an igneous rock. So if we're searching for a period composition to sand cast with, we've found it in "De La Pirotechnia". However we should continue our examination of the period compositions when it comes to casting.
So let's see what Benvenuto Cellini described in his "Treatise on Goldsmithing" published in 1568C.E. He explained that to make the clay he used for casting, add cloth frays to the clay and then he macerated the mixture and let it rot for a period of four months or longer. He doesn't give instructions about how to cast using sand. He also doesn't use a frame for casting.
So when we examine the compositions of casting investment, they all were using clay for lost wax casting. However Biringuccio is also using an igneous rock that is processed into sand or powder for impression molds.
After researching we discover that Green Sand can be traced to Biringuccio in 1540C.E. And a casting frame could be attributed to Theophilus in 1100C.E. when he cast a circular plate with the specific intentions of using it to form the bowl of a chalice. Now that the initial research has been done I shall return to "De La Pirotechnia" for further investigation.
Book VIII, The First Chapter "Various Methods of Making Powders in Which to Cast Bronze in the Small Art of Casting". After reading this chapter several times, I did get the gist of it. To make casting powder all of the ingredients are either burned or have been altered by exposure to high heat. So I thought about this observation and decided that I could generate a composition that most people should have access to. I first looked for a suitable replacement for "Tuff" and stumbled upon "Decomposed Granite". It is weathered granite that's starting to break down into particles such as gravel, sand and dust. It is used to form pathways in a fancy garden. I realized that using a very fine sieve would separate the dust and fine particles from this material. I decided that I wanted more than just granite dust in my composition, so I chose common items. Such as crushed brick, finely sifted top soil, ash from burned bone meal, hardwood charcoal and paper. All of these ingredients would be ground in a granite mortar & pestle, because most of us don't have a potters color mill.
Now to address the binder, which is "Magistery of Salt". Book VIII, The Second Chapter "The Method of Preparing the Salt for Giving the Magistery to the Casting Powders". He gives instructions for melting the salt in a rough clay pot. This is a very important step because it will alter the salts composition and there is a footnote that further explains it will introduce Sodium Silicate by reaction with the clay. So I thought about it and came up with a suitable replacement for the clay pot with a lid. I will use the saucer bottoms normally used for flower pots and simply flip one over to create a lid for the other saucer and place the kosher salt inside. This is supposed to be covered with charcoal and then burned until the salt melts**. I realized that I could use the same charcoal fire for double duty and sprinkle the hot coals with the bone meal powder, this should burn it quite well. After this has been accomplished I will break up the saucers to separate the salt from them after it is cool. The salt will then be placed in a metal pot and boiled with spring water to dissolve it. Once it has dissolved, allow it to settle and cool. This is used to moisten the casting powders.
In conclusion, we have discovered upon closer examination that casting with sand took place during the Renaissance Period and prior to that clay was used to make the impression molds for casting. So yes, casting with sand is late period and can be attributed to Vannoccio Biringuccio, however a casting frame was used by Theophilus Presbyter during the Medieval period. This should clarify any misunderstanding about sand casting.
* "I would never cast molten metal into something that is Damp. The steam could very easily eject the molten metal from the mold".
** "Molten Salt is very dangerous and can burn you very badly, use caution. Salt melts at 1545.8° F".
Celtic Craftsmanship in Bronze
1980 H.E. Kilbride-Jones
Theophilus, On Divers Arts
1979 Dover Books
The Pirotechnia of Vannoccio Biringuccio
1959 Dover Books
ISBN 10: 0-486-26134-4
The Treatise of Benvenuto Cellini on Goldsmithing and Sculpture
2006 Kessinger Publishing
ISBN 10: 1428604308
Copyright 2015 by Timothy S. Chapman, 8217 winters Lane. Mason, Ohio 45040. <tschapman1 at gmail.com>. Permission is granted for republication in SCA-related publications, provided the author is credited. Addresses change, but a reasonable attempt should be made to ensure that the author is notified of the publication and if possible receives a copy.
If this article is reprinted in a publication, please place a notice in the publication that you found this article in the Florilegium. I would also appreciate an email to myself, so that I can track which articles are being reprinted. Thanks. -Stefan.