Tamahagane Colors?

[Taz575]

I have question about Tamahagane and figured someone here may know.  The colors in the steel I think signify the impurities, but does anyone know how to match the color with the impurity?  Ie the Purple color is one element, pink is another, blue is another element, etc?   I got some chunks of Tamahagane and some of them have an iridescent blue/pink mixture, other pieces have a bright flat pink, cobalt, blues, purple, golds, silver, shiny pinks, etc.  

 

 

[Fuuten]

I don't think the colors are directly related to the materials. Also the quality of the tamahagane as far as i understand it has to do with the composition of the material / iron and not so much with the color it has, though a brighter color might indicate a higher grade or less impurities, it doesn't say much about the carbon content, which is as far as i understand it what they sort for their basic forging.

[ROKUJURO]

Iron alloys can show a range of colours depending on the temperature which they had when they were taken out of the fire and cooled. Colours have nothing to do with impuritiers or alloying metals.

See http://www.metallograf.de/start.htm?/begriffe/tab-farben.htm 

[Taz575]

The coloring is not tempering related from what I see.  Where the colors are, the material is often a completely different texture, like something melted there and is often smooth and glossy.  There are spots and flecks of color and larger pools of color.  Also, pink/salmon is not a typical color of tempering, which is straw to blue to purple. and it will effect a large area, not tiny spots.   Most tamahagane testing I have seen is after it's forged out, not in its raw state.

 

[Ken-Hawaii]

The information I got from a tosho was that he chose the most-colorful parts of the tamahagane, especially the blue, but couldn't tell me specifically why, other than that's what his father told him to use.

 

Ken

 

[IJASWORDS]

For my sins, I have a degree in metallurgy (the science of metals). Ferrous materials may show differing surface colours as combination of heat and oxygen.  

[ROKUJURO]

Tim,

I did not say the colours were tempering-related, but temperature. As IJASWORDS (please add your name!) writes correctly, mainly the reaction of the metal with oxygen causes the colouring. Under special conditions, there can be additional influences like metal vapours, which can produce other colours. 

By the way, your pictures of TAMAHAGANE samples show a lot of slag which may classify it as lower quality. Higher quality often is more colourful - one of the reasons why it is called 'jewel steel'.

[IJASWORDS]

Sorry forgot, name is Neil.

Notice colouration is in voids exposed to oxygen, where as broken surface is silver. Neil.

[Taz575]

On that piece, correct. Other pieces have some colors on the surface, other times it is within pockets in the piece of steel, which lead me to believe that there was some sort of impurity in that pocket that melted out, but left some material behind.  The pink is more on the surface, usually at the ends of more pointy material.

 

When I watched the video of Walter Sorrells and Jesus Hernandez making their own tamahagane, theirs did not seem to have any color pockets to it at all, but they started with a more pure ore, so I thought that the impurities (minerals and other) in the steel was responsible for the color areas.

 

In High School, we did a chemical burn test where we burned various elements and recorded the flames color when we did so and there were all different colors, so when I saw the tamahagana with the colors to it, I thought back to High School where different materials burned with different colored flames and wondered if different elements melted into different colors as well.

 

The reason why I was asking was I was thinking of trying to make my own tamahagane and focus on getting more colors to it by adding different minerals/elements to it, but it sounds like that would be hard to do!

[ROKUJURO]

Tim;

 

we have had a lengthy thread on this subject (http://www.militaria.co.za/nmb/topic/20975-availability-of-raw-material/). As the iron will not melt to a liquified state, it is not possible to transfer other elements into it except as very low amounts (impurities). You cannot produce alloys by this method. 

 

[Taz575]

Good read on that thread!  That explained things a bit more. 

[IJASWORDS]

Hi Tim, the flame colours you saw a school in the Bunsen Burner were the coloured oxide products in the oxidizing part of the flame. Jean is correct, normally to alloy iron/steel, foundries add "master alloys" like ferromanganese or ferrosilicon, where the alloying elements are already combined with iron, and therefor melt and combine easier.

BUT, alloying elements affect heat treatment, work ability and welding, all of which are important in the NIHONTO manufacturing process. Carbon hardens iron into steel, by entering the irons grain structure. Too much carbon makes iron brittle.

My love for Japanese swords was ignited as a student metallurgist, studying iron/steel and seeing what the Chinese and Japanese did a thousand years ago with hammer welding and differential heat treatment. Took Europe centuries to even come close to the technology.

I am sure many books have been written about the subject. Neil.