Zirconium Carbide (ZrC) is a very really hard refractory ceramic material. It is often processed by sintering. It's got the looks of a gray metallic powder with cubic crystal structure. The color variations to blue and black at better length from your resistor, and these darker crystals are less pure. https://kameronjkiif.elbloglibre.com/34349562/detailed-notes-on-titanium-cutting