kivis Posted January 24, 2012 Share #1 Posted January 24, 2012 Advertisement (gone after registration) I thought Chrome is silver in color. Here I found this definition: Black chrome is usually plated over bright nickel or matte nickel in the same manner as decorative chrome. Black chrome is not quite as hard or wear resistant as normal nickel/chrome and it is not lustrous. The finish may waxed or oiled to improve the final appearance. Black chrome offers high solar absorption and low emissivity useful in solar panel applications. It is also used for optical components, gun sights and components, lighting and plumbing fixtures and some automotive parts. Here what I found in Wikepedia: Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardness. Link to post Share on other sites More sharing options...
Advertisement Posted January 24, 2012 Posted January 24, 2012 Hi kivis, Take a look here What is black chrome anyway?. I'm sure you'll find what you were looking for!
payasam Posted January 24, 2012 Share #2 Posted January 24, 2012 The top plate of the M6 is zinc, not brass as in the M3, M2 and M4, and black paint does not "take" on that. Thus black chrome. Chrome is of course more durable than paint, but some do not like the way it ages. Maybe a chemist will come along and tell you how chrome, ordinarily silver coloured, is made black. Link to post Share on other sites More sharing options...
Double Negative Posted January 24, 2012 Share #3 Posted January 24, 2012 I've always liked black chrome, such as on the older bodies. True, it doesn't age as "nicely" as black paint - for two reasons: - Most of the time, what's underneath is zinc, not brass - thus no "brassing" - It can get a little grey as it ages/oxidizes Still, it wears well in my experience with the M8. You could always apply "a product" to it to breath new life into it, if that's your thing. Link to post Share on other sites More sharing options...
adan Posted January 24, 2012 Share #4 Posted January 24, 2012 Here is a recipe for "black" chrome plating: Black Chrome Plating Process | eHow.com The difference from regular chrome plating seems to lie in the plating bath: "Silver" chrome plating uses chromic acid and sulphuric acid. Black chrome uses chromic acid, acetic acid, and barium acetate. ____________________ BTW - black lenses (if not painted black) are "anodized." Which is also an electrolytic process, except that the part to be coated is connected to the ANODE rather than the cathode. It is basically controlled oxidation of the aluminum surface, because aluminum oxide is more corrosion-resistant than pure aluminum. Aluminum normally always has a thin oxidized layer from exposure to air - anodizing just makes this natural layer thicker and stronger. Tweaking the bath (acidity, type of acid used, and temperature), and the voltage and current, allows for "coloring" the aluminum oxide layer produced, including black. Link to post Share on other sites More sharing options...
Jeff S Posted January 24, 2012 Share #5 Posted January 24, 2012 ...normally always... This phrasing could be added to this thread. <g> On the surface (so to speak), black chrome would seem to be another oxymoron, until one understands the technical aspects that you and others present. Jeff Link to post Share on other sites More sharing options...
adan Posted January 24, 2012 Share #6 Posted January 24, 2012 Well, it is probably more of a tautology than an oxymoron. http://en.wikipedia.org/wiki/Tautology_(rhetoric) But the journalist in me "normally always" wants to avoid categorical statements - there may exist somewhere a freshly-cut piece of aluminum on which the surface layer has not yet oxidised. Link to post Share on other sites More sharing options...
Jeff S Posted January 24, 2012 Share #7 Posted January 24, 2012 Advertisement (gone after registration) Well, it is probably more of a tautology than an oxymoron. Somewhere between the two (since 'usually' - akin to 'normally' - isn't the same as always; nor is it the opposite)...so let's call it an oxytology. Jeff Link to post Share on other sites More sharing options...
Studio58 Posted January 24, 2012 Share #8 Posted January 24, 2012 The top plate of the M6 is zinc, not brass Unless of course the M6 is, (like mine) a Millennium model. That is brass top plate, black paint. Link to post Share on other sites More sharing options...
digbyhp Posted January 25, 2012 Share #9 Posted January 25, 2012 I recently acquired a second M7, black chrome, but had dithered over whether to get a black paint model (I love the brassing) or the black chrome. I'm hoping I live long enough, use the camera enough, so that the brass will come up through the zinc and through the black chrome.......don't fancy my chances. But I do like the red dot against the matte black. Link to post Share on other sites More sharing options...
payasam Posted January 25, 2012 Share #10 Posted January 25, 2012 Imaginary brass is easy to imagine. Unless all M7s are brass, that is: in which case there will be no zinc. Link to post Share on other sites More sharing options...
digbyhp Posted January 25, 2012 Share #11 Posted January 25, 2012 Imaginary brass is easy to imagine. Unless all M7s are brass, that is: in which case there will be no zinc. I seem to remember reading somewhere on the forum that all M7s use brass top and bottom plates, then there is a zinc coating and then the chrome. Link to post Share on other sites More sharing options...
payasam Posted January 25, 2012 Share #12 Posted January 25, 2012 You are correct. On Leica FAQ — M body repaint I found that "only older brass body Ms can be repainted (along with the new M7 or MP, now Leica have gone back to using brass)." And, on http://www.rangefinderforum.com/forums/archive/index.php/t-61361.html: "ALL Leica M7 topcovers (and their baseplates) are made from brass. As has already been pointed out here, there is a thin layer is [of] zinc under the black chrome (and silver too for that matter). The finish will eventually wear down to brass." I apologise. Link to post Share on other sites More sharing options...
digbyhp Posted January 25, 2012 Share #13 Posted January 25, 2012 Don't apologise, I'm thrilled that at some point I might get brassing on my camera without having had to pay for black paint on an a-la-carte Link to post Share on other sites More sharing options...
lars_bergquist Posted January 25, 2012 Share #14 Posted January 25, 2012 The reason why 'shiny' chromium can be black is small particle size. Silver too is a shiny bright metal, but the silver in my negs and prints was distinctly black ... same reason. The old man from the Wild Wet Darkroom Link to post Share on other sites More sharing options...
delander † Posted January 25, 2012 Share #15 Posted January 25, 2012 You are correct. On Leica FAQ — M body repaint I found that "only older brass body Ms can be repainted (along with the new M7 or MP, now Leica have gone back to using brass)." And, on http://www.rangefinderforum.com/forums/archive/index.php/t-61361.html: "ALL Leica M7 topcovers (and their baseplates) are made from brass. As has already been pointed out here, there is a thin layer is [of] zinc under the black chrome (and silver too for that matter). The finish will eventually wear down to brass." I apologise. I cant imagine that there is any zinc directly under the black chrome. Zinc is a reactive metal it would be severely attacked in the black chrome plating bath. To plate black chrome (or ordinary chrome) onto brass it is normal practice to plate the brass firstly with copper, then with nickel and finally with chrome. Black chrome is a discontinuous deposit of chromium metal mixed with chromium oxides and possibly other chromium compounds. Jeff Link to post Share on other sites More sharing options...
payasam Posted January 25, 2012 Share #16 Posted January 25, 2012 I too thought that the base was overlaid with copper and then nickel before being chrome plated. Maybe I should speak to a cousin who is a metallurgist. Link to post Share on other sites More sharing options...
jdlaing Posted January 25, 2012 Share #17 Posted January 25, 2012 I too thought that the base was overlaid with copper and then nickel before being chrome plated. Maybe I should speak to a cousin who is a metallurgist. I'll be darned. Hiya Payasam! Link to post Share on other sites More sharing options...
payasam Posted January 25, 2012 Share #18 Posted January 25, 2012 Hello, jdlaing. What's with the darning? Pico, please see my posts later than the one you quote. Link to post Share on other sites More sharing options...
jdlaing Posted January 26, 2012 Share #19 Posted January 26, 2012 Hello, jdlaing. What's with the darning? Pico, please see my posts later than the one you quote. Hadn't seen you in a loooong time. We go back a few years. Fourthirds wise that is. Link to post Share on other sites More sharing options...
jaques Posted January 26, 2012 Share #20 Posted January 26, 2012 I cant imagine that there is any zinc directly under the black chrome. Zinc is a reactive metal it would be severely attacked in the black chrome plating bath. My m6 camera is in very nice cosmetic condition with few signs of use and no wear on the black 'chrome'. However on the top plate there are some tiny 'bubbles' in the surface. Apparently these were a known issue with black chrome M6's. Perhaps this is related to the zinc layer? I have often wondered about how metal is treated on guns- giving a nice black finish- and wondered why we couldn't have a camera with a finish like that...? Link to post Share on other sites More sharing options...
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