Black quarry tiles - or is it just dirt??

[PrioryCottage]

This is probably a really stupid question, apologies, but I really need some advice.

When we moved into our house two months ago we lifted a manky bit of old carpet to reveal some beautiful, albeit well worn, black tiles.

However, every time they are washed they appear to be a little more red. So I am wondering if the black is actually years and years of dirt and damp from being under a carpet, or if they were maybe treated with something that made them black, like paint, but no paint.

Weirdly, there are also similar tiles on the fireplace, which are also black, but were never covered with carpet, so look a lot better:

So anyone have any ideas what the deal is with these tiles? Should they be red or should they be black?

 

[plasticpigeon]

Could be either, how about giving just one a really good scrub!

 

[Lime]

Stain, paint, oil or varnish rather than dirt I think.
Could even be the remains of milk.
The dark effect is too uniform to be just dirt.
It looks quite old too, but not centuries.
However where the wear has taken place they are definitely red.

 

[FamilyWiggs]

Those are beautiful tiles... lucky you.

Odd that the grouting is not discoloured in the same way.

I'd be inclined to leave them and let your feet clean them up, rather than scrub them straightaway.

 

[Flyfisher]

The grouting also stood out to me as an indicator that the black colouring of the tiles is not just dirt.

Could the tiles have been treated with something to make them black, which has been worn off in places to reveal the underlying red?

But what a lovely find.

 

[Gareth Hughes]

You should all know by now that there's no such thing as dirt.
There's patina.

 

[88v8]

There are black quarries. In this batch we bought, some were coal black, some veered more towards red. The black was fired in though, not an after-effect.
We used them here to make a breathing border in our sitting room, where a streamlet runs into one corner a few inches below the floor. Hence the wide joints in quarries & slabs.

Ivor