Explanation. It’s a dryer drum – stainless steel. It is reported that when stainless steel is heated more chromium diffuses towards the surface and more oxygen diffuses in from the air. The thin film of chromium oxide, which passivates the surface, increases in thickness.

ANU Student Capter of Optica and SPIE IDL2025 event - student presenters and chapter office bearers @optica.org @idlofficial.bsky.social @ausphysics.bsky.social

Please reply with your explanations. For those keen to learn more of such beautiful optical phenomena watch the replies. I’ll chip in in a couple of days to acknowledge those who worked it out and add to the explanation if needed.

Happy International #lightday2025 . Here’s an optics-in-the-home puzzle to get those with optics knowledge thinking. What’s the explanation for the attached image? @idlofficial.bsky.social #lightday2025 @ausphysics.bsky.social @david-optica.bsky.social @optica.org

Happy International Day of Light, May 16th 2025. There was rain but no rainbows in Sydney this morning. So here’s some wet leaves photographed under a rainbow umbrella instead. @idlofficial.bsky.social #lightday2025 @ausphysics.bsky.social @david-optica.bsky.social @optica.org

🧵💡 May 16 #lightday2025 Event Spotlight 🎊 🇦🇺 #Australia🇦🇺 🔹 A unique science and art poster exhibition by students and researchers highlighting their work in optics and photonics organised by The University of Sydney, SPIE, Optica Student Chapter ➡️ docs.google.com/forms/d/e/1F... @unesco.org

🔹 From laser to teleporter – will dreams become reality? A Public lecture by Prof. Hans Bachor organised by The Australian National University, @optica.org and SPIE Student Chapter and TMOS ➡️ anuosa.wordpress.com/2025/05/12/i...