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Fwd: Copper ingots

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  • Ted Sojka
    Here is a follow up to the copper pour at the U of Minnesota message and photos I sent out yesterday.
    Message 1 of 1 , Jan 15, 2013
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      Here is a follow up to the copper "pour" at the U of Minnesota message and photos I sent out yesterday.
      Begin forwarded message:

      Hi Ted,

           Thanks for the note about the email address. I took your hotmail address off my list so that I am using the correct one for you.

           Just to give you a little recap of this copper ingot project from the perspective of looking back over the past few months. We started off with an idea basically and have been successful (largely due to your inputs) in getting the relevant pieces put together to make it work. 

           1. I have now located the actual types, weights and accurate dimensions of the ingots from the Uluburun ship wreck. As I mentioned to Kelly, I had the very good fortune to get in contact with the assistant curator of 'Beyond Babylon' and was able to see this exhibit at the Metropolitan Museum of Art in New York the day it was closing, March 15th, 2009.  All four of the copper ingot types were displayed and I had a chance to view all of them personally in the display case. That was somewhat unnerving to look at a manufactured trade good that is still as useful today as it was 3500 years ago when it disappeared beneath the sea surface. There is a fundamental element of human utility in many basic materials and copper has to be one of the items high up on that list.

           2. Kelly and I have had a number of conversations regarding the appropriate casting techniques that we are going to try. Our goal is to make two or three of the large standard (four protrusion) hide ingots and one each of the others.

           3. I have located a source of used pure copper for $1.63 a pound. It is from a metal recycler in Rapid City, SD. I plan to purchase about 200-250 pounds worth to make the ingots from. I will haul the material over from South Dakota in my truck.

           4. We plan to pour both pure and slightly alloyed ingots to check on the castability of the various materials and confirm that the slightly alloyed material is actually easier to cast. Apparently pure copper is difficult to cast smoothly. From what I saw of the ingots, the air face in an open casting mold has air inclusions that make for a rough surface. The air exposed face (as opposed to the mold contained side) solidifies much more rapidly and often is lumpy or bubbly from escaping gases that are either trapped or bubble rupture just as the metal passes its melting point and the crystalline structure flashes to solid. At the surface this happens very rapidly depending on the exposed surface air interface temperature. The surface of the ingots that I saw were rough. Having said that, some of this may have been caused due to an anodic reaction in salt water over the course of 35 centuries. I am not really sure about this but we should have a clearer idea after the metal is cast.

           5. The target cast weight of the standard hide ingots is one talent (pre Biblical period indexed weight equal to about 60 pounds (U.S. measure). There was a variation in this amount. Among the copper ingots from the shipwreck the average was 63.4 pounds, if my memory serves correctly. We will shoot for a poured target weight very close to that amount and are going to achieve it through a mass to mass conversion index shown in the appendix of 'Hotmetal' by Wayne Potratz (Univ. of Mn.). The mold positive will probably be made from foam or pine with the mass index conversion done to adjust the volume for the desired target weight. The mathematical model is constrained by the known height/width dimensions and the mass. Therefore the only adjustment available to arrive at a target mass is the thickness.

           6. When we have the ingots finished we will be able to use them for educational purposes and also for calibrating various types of sonar. That will allow a sophisticated sonar unit with computer interface to have the ingot shape and acoustic reflective characteristics stored in its article comparative data base. I had some detailed discussions yesterday with a geophysicist/civil engineer from  Kongsberg Mesotech at the GHOST SHIPS FESTIVAL in Milwaukee, WI yesterday.

           7. With the recreated artifacts in hand and the electronic signatures available we have a solid footing to operate from in looking for these items as submerged relics.
      To the best of my knowledge that is the first time that this has been done, at least in this hemisphere.


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