Figured I would update. I tried Poly-Metal Finishing on my last order, good customer service, good turnaround time, but I wasn’t very happy with the depth of the color. They didn’t offer a bright dip pre treatment (electropolish) and it definitely showed in the final look of the part. Just didn’t have that same luster/shine I’m used to. Not slandering them, great experience and if I have other work in the future I will definitely be using them. But my product line needs the deep shine that seems to only be achieved with bright dip.
I have another batch at Light Metals Coloring in Southington CT, they are WAY more expensive but they do offer the bright dip so fingers crossed it comes back looking good. So expensive that I may never go back unless the quality and turnaround time blows me away.
The search continues. Going to explore 3rd party electropolish. I would consider using two separate vendors for electropolish and anodizing.
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not a good idea to split the polish and anodize, parts will slightly oxidize after polished, its pure Al on the surface, it is inevitable once they are polished dried and shipped to you (unless some sort of oil is used or something else to protect pure Al from oxygen in air)
then these parts go to anodizer, who will rack them and then degrease, maybe short etch, deox and anodize, this degrease+etch will make the part very slightly matte, you might try skipping the short etch, but results might not be very consistent then
so best practice is: to do everything in a single process, because after the parts are polished (be it bright dip or electropolish - 2 different things btw), they never are exposed to air and get chance to oxidize, there is a water film protecting it at all times till they are finally sealed, rinsed and dried
also every racking/deracking is a part damage risk and will leave more score marks (also called rack marks) than a single process would
edit: also there is a risk of nasty pit corrosion when polished to pure Al and exposed to air/moisture and stored in an inappropriate way, some paper has chlorine in it, enough to cause deep pits on Al if left in contact with the part, especially evident if parts were packaged wet
the way I know is when tumbled parts (it also leaves pretty clean and degreased Al surface) got shipped to me, they had blind holes that were never blown out with air and dried, they just got wiped down and packaged with paper towels, those soaked up all the remaining water (not clean water, but whatever was in the tumbler) and corroded the parts, and buffing with scotchbrite won't solve the problem, you need to remove 0.1~0.2mm from the part, the pits are that deep, they look like tiny pin holes, but they are very deep, and will look like black dots after regular clear anodizing