Does scale on the zincs affect effectivness?

[Greg]

When I changed my zincs earlier this year, this is how they looked:

They are all almost full size, but have this flakey, scaly coating on them. I was wondering if that is insulating the zinc and reducing the effectiveness of them. When I scraped it off with a razor blade, they were a little pitted, but it got right down to nice shiny zinc. Should I be taking them out once a month and scraping them?

 

[JohnEGraham]

I assume that they are in your diesel engine? anyone knows if a standard gas 350 engine has anything like it? JG

 

[compensation]

The 3 on the left look pretty normal for zincs that are ready or near ready to be changed. The fourth from the left is another story. It is normal for pencil zincs to thin out and then gradually erode from the tip to the plug base. The 4th from the left looks almost new, which could mean that there was no electrical bond between the zinc and the heat exchanger. I would be most concerned with why this one is NOT eroding, more than that the others are eroding.