[Skid Marx]

This was actually a 'legit' project. The teacher supplied the rusted steel, It was up to us to recycle it. Everyone in the class had a different method. I spent a couple of days with a smooth file and an aluminum bar, because I'm a knucklehead. The teacher reminded me that aluminum was more expensive per unit than iron, but he had to demonstrate it anyway, even though he knew what would happen. It was irresistible. You'd understand. Had about a pound of finely grained product, used maybe half of it. Also used mag. ribbon to light it directly. The results flared to the ceiling and spalled all over the place. My friend Bill's method used HCl and limestone granules, it blew up in his face.

[Myrddin]

Fine aluminum dust and fine iron dust are typically employed to make flash powder. The iron makes a yellow colored shower of sparks. Aluminum tends to bright white. It's not surprising that you ended up with a "flare" instead of the typical smoldering, smoking blob of a thermite reaction. A little strontium nitrate makes for a red color. That's what is used in road flares. Once upon a time, I was a bit more fluent in which compounds produce specific colors.