What is this blistering on top of my Pentax KX?

[Jross1297]

Hello I’ve tried posting these photos and I’m getting many different answers as to what it is. There’s these tiny little bumps all over the top plate of my Pentax KX. It looks like what happens to Leicas but I heard it’s because Leicas top plates are plated with zinc with corrodes over time but I know Pentax at this time used brass. Is this just the paint failing or a more destructive corrosion? If it’s just cosmetic I can live with it but I don’t want the top plate to detoriate over time and start pitting NOTE the flash makes the bumps appear white but they are not in person

 

[Jross1297]

Don’t know why it’s not letting me upload the photos

 

[runswithsizzers]

I'm not sure, but there may be some minimum number of posts for new member before you can post photos?

Is the metal top plate on your Pentax KX black or silver? I'm pretty sure the top plate is brass in either case, but the silver ones are plated, and the black ones are probably painted?

 

[Jross1297]

I'm not sure, but there may be some minimum number of posts for new member before you can post photos?

Is the metal top plate on your Pentax KX black or silver? I'm pretty sure the top plate is brass in either case, but the silver ones are plated, and the black ones are probably painted?

It’s black, and I can chip off the little bumps with my finger nail and it’s show the brass underneath

 

[GregY]

Leica M2 & M3 with brass top sheets, black paint had bubbling issues....

 

[MattKing]

Don’t know why it’s not letting me upload the photos

Welcome to Photrio.

I always suggest to people who are struggling with this that they first resize the photos to jpegs with quality less than 100%, with dimensions of 1000 - 1200 pixels on the long dimension.

 

[koraks]

Don’t know why it’s not letting me upload the photos

Welcome to Photrio! Sorry to hear you're having problems uploading photos. Perhaps there's a solution here: https://www.photrio.com/forum/threa...s-and-avoid-size-limit-problems.211668/unread

 

[Ian C]

In some uses, metal that appears to be of one type is plated over a cheaper material. For example, many zinc or zinc-aluminum alloy castings are first copper plated, then given a final plating of chromium or other metal.

I used the following search string with Google:

“How are zinc or zinc-aluminum castings prepared for final plating of chromium or other metals?”

Google Search

It returns interesting results that agree with my observations in which I noticed areas where the top plating had been damaged or corroded to reveal a layer of copper plating over the base metal of zinc or zinc-aluminum alloy.

There are several different lower-cost commercial casting alloys in which the base metal is sequentially coated to make a cheap part look elegant and to give it at least some protection from corrosion.

This used to be a common practice on both interior and exterior metal decorations on automobiles, such as hood ornaments and interior dashboard trim. This is especially seen with exterior parts. Over time and with the exposure to de-icing road salt in colder winter climates, the plating eventually bubbles and separates where salt has entered through tiny gaps in the coatings.

The base metal doesn’t have to be zine or zinc-aluminum alloy. I have an old scissors, obviously steel, and probably more than 60 years old, that has a bubbled chrome plating like this. Another item that shows this is the bottom surface of a chrome-plated Slik Quick Release Post from my U-212 tripod. That the base metal appears to be brass (alloy of copper & zinc), doesn’t preclude this type of “bubbling” of the plating, such as noted on the Pentax camera.

Other useful Google search strings for this phenomenon are:

“Blistering in zinc or zinc-aluminum castings”

“What causes blistering in Leica M6 top plates?”