This post documents the machining and torch-coloring of custom titanium screws for an all-titanium sculpture. The maker walks through the full process: turning the screws on a lathe, milling a quad-drive feature into the head (a four-lobed drive recess as an aesthetic alternative to Phillips or Torx), and then using an open flame to develop interference colors on the surface. The open question they pose to the community is a genuinely interesting design choice: should the milled drive feature be cut before or after coloring, to maximize visual contrast between the polished recess and the colored surrounding metal?

What makes this post educational is the physics behind titanium anodizing-by-heat. Titanium grows a transparent oxide layer when heated (or anodized electrically). The thickness of that oxide depends directly on temperature, and the resulting color is not pigment — it's thin-film interference, the same phenomenon that makes oil slicks and soap bubbles iridescent. As the oxide grows, different wavelengths of light reflected from the top and bottom of the layer interfere constructively or destructively, producing a predictable color sequence:

• ~300°F: straw / light bronze
• ~400°F: purple
• ~500°F: deep blue
• ~600°F: light blue / teal
• ~700°F+: gold, pink, green (second-order colors)

A few practical lessons readers can pull from the thread:

• Surface prep matters more than the flame. Fingerprints, oils, and abrasive scratches all show through the oxide because the layer is only nanometers thick. Clean the part and finish it consistently before coloring.
• Torch coloring is less repeatable than electrical anodizing. A propane or MAPP torch gives you the look quickly but with uneven heat zones — you'll see banded colors on a single screw. For matched sets, an electrical anodizer (a DC supply and a phosphate bath) gives precise voltage-to-color control.
• Cutting after coloring removes the oxide locally, exposing bare silver titanium. That's exactly why the maker is considering post-color milling — the contrast between a colored field and a freshly cut bright drive recess is much sharper than coloring over a pre-cut feature where heat creeps into the recess.
• Heat is cumulative. Once you overshoot a color, you cannot go back without re-polishing — the oxide only grows thicker, never thinner.

It's a great window into how machinists treat fasteners as design elements, not just hardware.