Polished porcelain tiles

[thompsonbrown]

http://www.tilersforums.com/attachm...1389817664-polished-porcelain-tiles-image.jpg

So you can zoom in a bit.

Most of the dark patches look as if they run in lines through several tiles.
This would suggest to me that its trapped moisture between the tile and your protective covering. Try using a hair dryer on a small section and see what its like the next day.

 

[widler]

Get a floor polisher form a hire shop,try that,it might need a bit of gentle aggression

 

[Welshwizard63]

Tried 2kw hairdryer for half hour but made no difference tried stripping again and cleaning with acid detergent and tiles darken down when wet but lighten up when they dry