Temper color on titanium

Titanium reacts with oxygen as soon as it gets hot. The temper color tells you how much oxygen the metal has absorbed: the darker the color, the more. Silver and light straw yellow are okay, blue or gray means the material is embrittled and the weld can crack. Therefore, you must always weld titanium with shielding gas and let the weld cool under shielding gas. The root side also needs protection, otherwise it oxidizes from behind. If you see dark temper colors, you must completely grind the area away until the metal is bright again. Use a stainless steel brush or burr, not a regular steel brush.