Monthly Archives: October 2012

The Reasons Porous Molds Could be Used In Egyptian Casting

The British Museum-Ancient Egyptian Cat

The British Museum-Ancient Egyptian Cat (Photo credit: AKinsey Foto)

English: Liquid bronze at 1200°C is poured int...

English: Liquid bronze at 1200°C is poured into the dried and empty casting mold. (Photo credit: Wikipedia)

English: Melting metal in a ladle for casting ...

English: Melting metal in a ladle for casting Deutsch: Metall wird in einer Gießpfanne zum Schmelzen gebracht. (Photo credit: Wikipedia)

Egyptian bronze art, and many of their swords were made by casting into clay molds. Clay, though, is very porous, and so are many other casting materials used then as well as today. So why doesn’t the molten metal seep into the pores and adhere to the mold itself? Two reasons.

 

One reason is that gases are formed around the molten metal, such as oxygen forming a compound, or some of the molecules superheated into gaseous form, or many other such things that form on or over the surface of the molten metal. Anyway, this gas goes in between the metal and the mold, pushing the metal back in a super-thin layer, so the metal still takes on the details of the mold, without seeping into the pores.

The second reason is that the surface tension of many metals is so great that it will not seep into the pores, and yet still not too much so the metal could flow into the finest of details in the mold.

So when the Egyptians cast their metals, luckily they did not have such great surface tension that would prevent detailed casting, but gold, silver, copper and bronze were all metals that had good surface tension, which kept the metal from seeping into the pores. Also, the tension could keep the metal smooth against the rough mold wall, and so make polishing later on much easier, producing the fine bronze sculptures that are dug up today and found inside the pyramids.

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The 2012 Shasta County Gem Show

On October 20 and 21 was the Shasta Gem and Mineral show, and here is a list of impressions I had of it:

Surprised at the number of stalls and people

The size of the crystals

The colors

The variety of silversmithing styles

The variety of affordable stones, such as emeralds, rubies, and tourmalines

The number of people I knew from the gem club.

The kindness of those people,

And the feeling of being home.

 

The Secrets Behind Steel

Blast furnaces of Třinec Iron and Steel Works.

Molten (Photo credit: scottwills)

For Iron to be extracted from the raw ore

MoltenA carbon steel knife

Molten (Photo credit: scottwills)(basically Iron Oxide), it has to be heated to the point where the iron basically melts off the oxygen, where it can be gathered by the smelters at the bottom of the smelting pot. As it goes through the process of smelting, the Iron picks up a bunch of carbon instead of oxygen. So once the iron cools down and the smelters remove it, it is about 2.5% or more carbon by weight.

That carbon forms microscopic crystals inside the iron; the crystals are hooked onto the iron. So if the crystals break the iron breaks as well: a brittle structure, which is a no-no in useful steel. The carbon crystals, though, are very hard, and they keep the iron from denting and bending so much.

So, basically, the carbon makes the steel harder, but at the same time makes it brittle. Let’s say we need the steel to make a sword. The Japanese would use hard, brittle iron for the edge of the sword, and strong, but dentable (less carbon, as the level of carbon content can vary throughout the smelting furnace, in this case less than .2%) iron for inside and back of the sword. This is so the edge of the blade does not dent and lose its razor-sharpness, and yet the whole thing does not shatter on impact. A different way is to have the whole sword made of metal half way in between. Once the iron has been extracted from the ore, most of it has a large amount of carbon, and so it goes through the bessemer process. In the bessemer process the iron is melted in a huge crucible, then air is blown in from the bottom, and the bubbles filter up through the molten metal. When the oxygen comes up, the carbon hooks onto the oxygen, and the float on up to the top of the molten mass, and then dissipate into the atmosphere, leaving the Iron with a perfect amount of carbon (the workers can decide the amount of carbon left by how long they keep the bubbles going through) in the steel, which is then poured into ingots and sent off to any number of steel working industries, or to a bladesmith who uses the steel to make a beautiful knife, which is bought by a young enthusiast who takes the knife home to use and to admire.

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My First Sale!

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Yesterday I got my first jewelry sale! I had my customer (a freind of mine) choose a stone to be set, then I soldered on the bezel (the strip of silver that holds in the stone). I let her choose the decoration and I finished soldering, sanding and polishing it. I did not sell it for much; only what the silver was worth, but it was my first sale!

Chromium Plating

Reflections on a motorcycle

Reflections on a motorcycle (Photo credit: Wikipedia)

English: Rear bumper on a 1971 Dodge Dart Pure (99.999%) chromium crystals, produced by ...

English: Rear bumper on a 1971 Dodge Dart (Photo credit: Wikipedia)

Have you ever looked at a shiny new car bumper and wondered how they got it to be so shiny and bright? It was done by being plated with chromium, a hard metal that takes a beautiful polish. Unfortunately, this metal cannot be used for the whole bumper, for two reasons: one, it is not cheap enough to be used so extensively, and two, it would dent WAY too easily for a car bumper. But how do they get the Chromium on? 

First, the steel bumper is cleaned and any oxides are sanded off and polished to a high brightness, then it is dumped into a liquid solution that transports elecrical currents well. Next to it, but not touching it, is a large lump of chromium in anionic form (meaning it has more electrons than protons, and so is negatively charged). Anyway, so they are both placed into the solution.

Now they are both hooked up with electricity, the bumper is hooked up with a positively charged flow and the chromium gets negative, and so the plating begins.

What happens? On the negative end, the elecricity sucks in oxygen, which hooks onto the chromium, becoming chromium oxide. This is now able to dissolve into the solution, which it does, and, being negative, is attracted where? To the car bumper. Once there against the car bumper, the positive electricity seperates the oxygen away, and the Chromium is plated evenly over the whole bumper, aligning exactly how the steel is aligned, and comes out polished to a beautiful finsh, and is sent to wherever cars are made.

One interesting fact is that whatever chromium is still in the solution when the bumper is lifted out forms little chromium crystals at the bottom, which are very bright and beautiful. Some tourists are allowed to keep these, otherwise they are just broken off and used again.

 

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Knapping

File:Arrowhead.jpgBefore the Europeans came to the new world with their iron knives and guns, all the Indians had were the branches above them and the stones beneath them, which were very useful. Combine those two things and you have the powerful bow and arrow, with a razor sharp obsidian tip on the end.

When the atoms in a particular mineral or other substance crystallize, they hook on to each other in a regular formation, enabling stronger bonding. If those atoms are not in crystalline form, but in random, or amorphous sequence, the product is not very strong, and in many cases, brittle. Obsidian is the same thing as glass, except not man-made.

Silica bonds strong, but all physical bonds can be broken, and once obsidian does break, it fractures into a very sharp, conchoidal edge, which can be used and made into spearheads and arrowheads. The process of flaking obsidian (or flint, which fractures very similarly to obsidian) to a sharp point is called knapping.

The knapper (or knapist, I suppose) chooses a piece of obsidian closest to the desired shape, sits down and puts a thick piece of cloth or leather on his/her thigh (you can probably guess why). Then the knapist puts the obsidian on his thigh, and uses a deer antler to flake off small chips of obsidian until the edge is sharp all around. Deer antler is best to use because the trick is to apply pressure to the obsidian until a flake flakes off, so a strong but not hard tool is best. Using, say, another stone to break off the flakes, you don’t have enough precision, and too much power, resulting in a crack down the middle. Anyway, the knapist breaks off flakes all around the piece, and then breaks off the top, using that piece, as shown below: (photo credit: Wikipedia)File:Levallois Preferencial-Animation.gifAfter that, the knapist finishes in the details, such as the grooves in the side to attach it to the arrowhead, and sells it to a young enthusiast, who either uses it to make his own arrow, or for decoration.