I went to see a job the other day, shower tray replacement. While I was there the homeowner pointed out that some tiles had discoloured. The tiles had been there over  15 years. What could have caused teh discolouration?

It only affected the bottom two rows of tiles, and a corner patch on the side wall about 3x4 tiles.

I thought batch difference, but this only recently happened. I then thought perhaps water ingress behind tile, but surely that would cause them to fall off the wall before it soaked thru to the other side of the glaze.

When feeling the affected tiles they were slightly "duller" as if they needed a good polishing.

The tiles had discoloured to a slightly darker shade.

This isnt a real problem i suppose anymore as its all getting ripped out with the tray, but its been puzzling me so any ideas?

btk

Perhaps they have used some kind of agressive cleaner that has damaged the glaze? Not sure what would do that.

Did she rub the shine off your err surfaces?