[Craig Sawyers]

Well, back when I was involved in this from a production standpoint, anodising - particularly black - was a nightmare. Depending on the condition of the bath, and the repeatability of the dying and sealing processes you could get anything from a nice deep black right the way to almost a blueish tinted black.

What precise colour you get is also strongly dependent on the aluminium alloy - so that is another process to control if you aim to get colour uniformity.

In the end we had a sample and the plater had a sample. They (it wasn't Metro Plating, by the way) were told that if the batch was visually different to the sample to strip it and replate. And we did rigorous QC on goods inwards.

Powder coating can be much more predictable from a colour point of view, and with a much wider colour palette, but it is difficult to get uniform coating on sharp corners and into deep profiles (like a heatsink).

There is another sneaky problem with extruded heatsinks - they are always slighly banana shaped. It is inherent in the extrusion process. Aavid cheerfully own up to that, and say if flatness of the device mounting surface is important (and why wouldn't it be?) that it should be post-machined flat. And they will do it for you - at an additional cost.

Craig