Blue’s Clues
Do you remember Blue’s Clues? Of course you do - you’re cultured! I’m struggling to tie this title choice into what I actually want to talk about.. but I’m sticking to it!
These two images really highlights the impact of different lighting conditions in metallography. If I had planned this out better, I’d have taken two images of the same spot at the same magnification. Hindsight…
Let’s talk about the specimen. I covered this sample previously in my Hello World blog. https://www.metallographytoday.com/blog-2-1/q2661y8lw1gh1pkr1wfwwou2ykf02h
316 Stainless steel
Additively manufactured
Etched with a very strange electrochemical procedure using a modified Kalling’s II.
I took these images on two different days. If you read my Hello World blog, you’d know I’ve had some… trouble with this specimen, to put it lightly. When I put this sample on the microscope this morning, it was BLUE. Like BLUE BLUE. I was amazed! And bewildered!
It looks so cool! But, WHYYYYYYY! I've been dealing with semi-porous samples lately and they can be tricky to etch. If you don’t thoroughly clean them after etching, acid can remain in the pores, leach out over time and continue to etch the surface. I’ve been having samples that mysteriously have their surfaces change over the course of hours/days. I’ve been attributing this to the aforementioned porosity problem and voodoo witchcraft. It’s hard to tell.
So when I saw this beautiful blue image on the monitor, I immediately jumped to conclusion that the phantom voodoo acid gnomes came out of the wall and etched my samples overnight. I went on a whole rant about it until my boss stopped me. “It’s just the lighting.”
The ligh-? No. It can’t be. I obviously checked that. Right? Shit, maybe I didn’t.
Obviously, we checked. It was the lighting. The mysterious blue image was created using ring lighting. When we switched back to coaxial lighting, the image returned to the green/brown camo looking color scheme. Normally, I image with coaxial. But when I restarted the microscope it defaulted to ring lighting.
Shawn Matt, the magnificent metallographer. Stumped by lighting condition in front of the boss.
What can you do! At least that particular mystery didn’t waste much time and further frustration. Still, I’ll have to solve the phantom voodoo acid gnome problem.
Unless…
It’s always been the ligh-? No. It can’t be. I’ve obviously been checking that. Right?
Blue’s… Clues?!
Here’s a bit more information for the initiated.
Ring Lighting: This involves a circular arrangement of lights around the lens that uniformly illuminates the sample from multiple angles, reducing shadows and providing even lighting. Ring lighting is particularly useful for observing surface textures and features with minimal glare, but it does not offer the depth of focus or resolution enhancements that confocal lighting provides.
Coaxial Lighting: Also known as epi-illumination or reflected light illumination, this technique directs light along the same axis as the viewing path. The light is reflected off the sample surface and back into the lens, making it ideal for examining flat, reflective surfaces and enhancing surface detail. Coaxial lighting is commonly used in metallurgical microscopes.
https://www.keyence.eu/ss/products/microscope/microscope_glossary/lighting/lateral_illumination.jsp
