Crosspost from Geekhack:
Hey guys!
A few clarifications on finish as well that I forgot to mention to Ellipse:
Durability is first and foremost a byproduct of how long the aluminum stays in the anodize tank. Second to this is minimizing angles on the piece, as the anodize is thinner around edges. Third is the material itself. You can make really tough Type II coatings, but I agree that Type III has the best abrasion/scratch resistance.
Cases like those seen from Tex or P0k3r are a simple Type II anodize, similar to the one seen on my amplifier above, usually with a pretreatment to bring back luster lost from the bead blast. Macbooks and iPhones also use a Type II in this fashion. Granted, I'm not discounting Type III, just making note that we use Type II anodize in our products daily with no ill effects. It's also important to note that a bead blast anodize without a bright dip pretreatment will give the keyboard chassis an AR lower receiver-style look, meaning more of a frosty gray than a true sheen, and will also show fingerprints more than other finishes. Bright dip pre-treatment brings back this luster. Think spray painting your car flat black (gray, dusty/frosty) versus a vinyl wrap or true semigloss satin.
I should also add that "clear" Type III hardcoat anodize will color the metal depending on the type of metal used. Source:
http://www.midstal.com/sft334/aluminum_reference_guide.pdfTank time also affects the coloration, as seen below:
These are all "clear" Type III hardcoat anodize with increasing coat thicknesses, from left to right.
SourceUpdate: You can indeed pretreat with phosphoric acid / bright dip / chemical polish prior to a Type III hard coat! I'd imagine it to be the be-all-end-all to durability without a sacrifice to aesthetics.
This said, I believe what we're looking for is something along these lines:
1. A case with no 90* angles (see first picture-- 0.015 radius ensures full coverage) around potential wear and abuse points to prevent chipping of the finish
2. An aluminum that satisfies those looking for a "clear" anodize, based on that table above
3. Glass bead blast medium, starting with a low psi and working upward until all surface abnormalities and marks are removed.
4. "Bright dip" phosphoric / chemical polish / pre-treatment of the aluminum to bring luster to the anodize
5. Type III hardcoat: clear (natural), black, gray, etc.
Metal finishing is extremely tribal knowledge; unfortunately I don't have any pictures of these possible finishes offhand outside of my amplifier posted above. Everything I've learned has been through rigorous research in my own DIY projects and visiting several metal finishing shops in my area. It would definitely be beneficial to get in contact with a shop that has samples of each of these styles to see what works best for everyone!