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cast_al-Cu_etched_KMnO4_NaOH.jpg

An alloy of 1.3% copper, 0.3% magnesium, and 0.3% manganese in aluminum, etched with potassium permanganate and lye.

So I woke up this morning all pumped up to blog about metallography. If you don’t already know, metallography is a type of scientific microimaging that involves mirror-polishing metal surfaces and then etching them with various reagents to reveal their microstructures, which are often of breathtaking beauty.

Griffith_Cannon_Flash_by_Frederick_E_Schmidt.jpg

“Griffith Cannon Flash,” by Dr. Frederick E. Schmidt, from the iron of a cannon used at Gettysburg.

Unfortunately, there aren’t a lot of these images online. ASM International, the big metallurgical professional society, has a large online database of metallographs, but it’s locked away behind a members-only paywall. Except for a couple of skimpy .PDFs (2007, 2008), even the winners of their annual International Metallographic Contest seem to go largely unpublicized.

Which is a shame, not only because the images themselves are so beautiful, but because they could inspire a whole culture of amateur and artistic metallographers that does not, as far as I can tell, presently exist. Which fact also surprises me, by the way, because the equipment and techniques of metallography are very accessible to amateurs, especially relative to other modern methods of materials analysis.

Grain_Structure_in_CC_cast_3304_aluminum_alloy.jpg

“Grain structure in CC cast 3304 aluminum alloy,” by Elana Naez.

If you know of anyone who’s making metallographs as a hobby or as a means of personal artistic expression, please drop me a link in the comments.

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. Anonymous says:

    just be aware that for almost all metallographic images…the color is added after the image has been captured. Most images will be grey in color since most metals are themselves grey. also… the taking a picture of a sample or the viewing of a sample on a microscope isnt that hard….the hard part is polishing a surface enough to get a good picture. that can require 1 micron polishing compound. I use normal sandpaper like abrasives to start out at and eventually work down to 1 micron

    It is a tedious process

    1. Michael He says:

      Obviously this person has never done color metallography! I don’t know of anyone that adds color to a micrograph after it is captures. The color can come from the material itself in as polished condition, from the way it is etched and/or the way it is illuminated on the microscope.

      For example, Fred’s “Griffith Cannon Flash” is likely etched with Klemm’s II and taken with polarized light with sensitive tint filter.

      There are a lot of published information on how to prepare color metallography.

  2. robot makes music says:

    Metals are crystal structures (due to the atomic nature of their bonding) so using crystalline metallography as a search term on google will return a few more images than you’ve currently got.

    To properly image these structures, unfortunately you need some very expensive microscopes to make the pictures like you see above. Under a regular light microscope, you don’t see very much on the surface of polished and etched metal surfaces – it mostly looks like a mirror.

    So you need special optical techniques, like Differential Interference Contrast (DIC), Darkfield, phase contrast or polarization to view the images in pseudocolor. And, unlike Anonymous above, the color isn’t “added after the image is captured” it’s a function of the microanalysis techniques – for instance, in DIC the light is split by polarization into two beams, bounced off the surface, and then recombined by a wollaston prism, that can be rotated to re-cohere the light into different colors, caused by constructive interference in the different wavelengths of light. What this means is the relatively flat and mirror-like surface will come alive with fantastic colors showing minute surface features that you can’t see with just plain old light. All the grain boundaries come alive with color.

    Did I mention you need a reflected light type microscope? You cannot use transmitted light for this unless you have an ultra-thin sample, and that’s mostly for geological rock samples, not metals – the only thing transmitted light can do for metals is show you that you have a properly prepared specimen ready to be viewed in a transmission electron microscope, a whole other crazy-ass field of metallurgical study.

    If you’d like more information, I can prepare a report for you on how to actually do this kinda stuff at home, what kind of microscope you’d need – we’re talking at least 1,000 if not more unless all you want is darkfield (which is just black and white with highlighted grain boundaries – light comes in from the sides and reflects off the edges of the etched grain boundaries, showing them with the mirror-like intensity but everything else is black).

    I had some DIC and darkfield images of metals that I flushed with the rest of my year 1 stuff…. sigh, I’m an idiot. I do have prints of them, however, that I can scan back in if you are interested. Drop a line to my email and I will do so and flickr them for you.