Oh, I agree. You've made a very good point. I still think that there could be something at play though when the dye is added that effects the overall strength of the anodizing. If so many parts per whatever is black dye instead of anodizing, you would think that would factor into the overall strength of the anodize, all else being equal. Such as true 2mm black vs. true 2mm Nat anodize.
Yes, but let me explain how the dye works. The dye is not included in the acid bath. The aluminum is first anodized which is basically just oxidizing the outer aluminum into aluminum oxide. This is changing the surface of the aluminum, both "growing" for lack of a better tern, into the aluminum and at the same time growing out from the surface in an equal proportion. In the case of a tube, the diameter will actually increase (which is important to note when dealing with tolerances). The aluminum oxide is not solid, but is filled with pores. Yes, very tiny little holes. At this point, you have Class 1. In order to get class 2, the part is now dipped in the dye which fills these pores. Then it is again dipped in a solution that seals the pores, thus trapping the dye in them. In Class 1, it will often get sealed as well, but this time without the dye in the pores.
There are some other reasons for moving away from Class 1, besides it being easier to cover up thin anodize, and that is that many flashlight manufacturers moved from 6061 to 7075 grade aluminum. 7075 can get a more bronze look to the anodizing while 6061 gets that nice dark green/gray if anodized to actual mil spec thickness. I don't mean to get into a discussion of 7075 vs. 6061 as they have different properties, both good and bad, depending on what the intended use is, but 6061 does anodize and look much better when done properly than does 7075 (my opinion, but if you like that dark green look, and I know I do, 6061 will get you there).
I have many lights, and I really wish I had kept my old natural HA Surefire E2E... I loved the look of that natural HA, and still do. If you look at photos of the original HDS lights (the ones without the bezel) like the EDC Basic or Ultimate, you will see the anodizing is a nice dark green. Then when you see the first production run of NovaTac... light gray, light green... crappo anodizing (and I screamed about it. Henry had already left NovaTac at that point and that's one area corners got cut much to my dismay). The second run from NT was... yep... Class 2.
The current HDS have MIL-A-8625F Type III Class 2, which is specified on the drawings. Yesterday we received some new heads from our machinist and we spent a good deal of time checking them over carefully. Everything from making sure the thread tolerances were in spec included the tiny screw holes no one ever sees after the electronics are added, how much current loss (there is always some) in the head where the threads are not anodized, and the anodize itself. We check carefully because if it is not in spec, we send them back. It was the first time for this machinist to do these heads though he has done other parts for us. They were absolutely perfect. The same day, I scrapped 464 reflectors because they didn't make the cut, but that wasn't the machinist, that was the vacuum reflective coating.
