What is black chrome anyway?

[payasam]

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Hadn't seen you in a loooong time.

We go back a few years.

Fourthirds wise that is.

 

We do indeed; and I apologise for my old and slow brain. The E System remains my weapon of choice in the digital world.

 

Jaques, my M6 is named Bubbles. I have read (without comprehension) that the defect is caused by imperfect preparation of the surface before plating. It is my impression that the metal used in guns is different and that its surface treatment is with a chemical process called "bluing".

[delander †]

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...?

 

The bubbles are where corrosion has penetrated all the layers of plating and got through to zinc based die casting which is corroding and producing voluminous corrosion products which are pushing up the plated layers.

 

Jeff

[pgk]

It is my impression that the metal used in guns is different and that its surface treatment is with a chemical process called "bluing".

Blued steel in fact - a very different treatment altogether. On a side note though, and for what its worth, I remember buying the matt black paint used for gun-sights to repaint the inside of a lens hood with - very effective, although I have no idea whether its still available

[Double Negative]

The bubbling on the M6 top plates are a bit of a common issue and caused by what delander describes above. I'm kind of curious what triggers it... Was it a batch of M6s? Due to environmental or usage conditions?

[pgk]

The bubbling on the M6 top plates are a bit of a common issue and caused by what delander describes above. I'm kind of curious what triggers it... Was it a batch of M6s? Due to environmental or usage conditions?

As an (educated) guess, I'd suspect that the problem is that the coating(s) over the zinc are to some degree porous - whether they all are is another matter. So eventually some water will penetrate down to the zinc and corrosion will take place. It may well be that some of this corrosion is electrolytic (due to dissimilar metals in contact with each other). Zinc is reactive and, especially if there is any electric current around, can be prone to corrosion - I use zinc anodes on underwater housings to prevent corrosion elsewhere. IMHO it isn't the best of materials to use especially when better are/were available.

[delander †]

PAul is correct. Although the Zinc based die casting is polished before plating it is invariably microporous and plating does not necessarily cover pores. Also the cleaning before plating is very important.

 

Jeff

[masjah]

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PAul is correct. Although the Zinc based die casting is polished before plating it is invariably microporous and plating does not necessarily cover pores. Also the cleaning before plating is very important.

 

Jeff

 

Forgive me for going slightly off-topic, but does this mean that galvanising bodies on posher cars is not the answer to all corrosion problems?

[pgk]

Forgive me for going slightly off-topic, but does this mean that galvanising bodies on posher cars is not the answer to all corrosion problems?

Galvanising steel protects against, but doesn't finally prevent, corrosion. The bodies should last a lot longer than none galvanised ones, although the way some (galvanised bodied cars) are driven its a total waste of time because they aren't likely to last long enough to corrode whether galvanised or not;).

[Michael Geschlecht]

Hello Everybody,

 

Some cars have zinc plugs in their underframes so the galvanic action eats away the plug instead of the steel. When the zinc is pretty much used up these plugs can be drilled out & replaced.

 

Chrome plating inside gun barrels goes back to anti-aircraft guns during WWII. So does lens coating of gunsights since attacking aircraft often came in w/ the Sun behind them in order that the brightness in general or flare in an optical system would make them harder to detect & shoot down. Also @ the same time submarines had the lenses in their periscopes coated.

 

I think black chrome on the outside of gun barrels as a more durable replacement for blueing began in the late 1950's or early 1960's. As blueing had replaced the brown protective coverings which preceeded it.

 

Best Regards,

 

Michael

[pico]

Nobody has ever seen a Leica body that was rusted/tarnished/eaten through due their shell material or coating.

 

But let that not distract us from worrying.

 

OMG! Should I wear Kid gloves?

[maurometallo]

I regard black chrome as the sexiest among all Leica finishes and I struggle to understand why so many people say that it ages ugly. I simply love those strands of silver peeping through the dark coating! I may be considered a poor connoisseur, but my M4-P, after 25 years of relentless use, looks very nice to me...

[jaques]

i agree completely- why did Leica make a black paint M9-P? That should have been black chrome. Even with the tiny bubbles (you can only see them from a few inches) my M6 has aged very gracefully and looks great. Leica should have tried a new black chrome finish. I think the demand says it all- the black paint does not seem to be a winner... people want chrome not paint. Leica should have tried new finish black chrome finish...