Crackle tile discolouration

[patmoore]

Hello

I was hoping someone might be able to advise. I’m having some crackle metro tiles installed and whilst they look lovely, as the tiler has gone about their business, I’ve checked and some of the tiles have this hue around the edges.

Can anyone suggest how this has happened? Trying to understand it.

[sammy.se]

Hi,
Are you sure it's not just where the glaze is a little bit thicker? Do you have a loose tile to compare it to?

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[patmoore]

Yeah I have few loose ones and none of them have any of that.

[ayjay]

I'm an amateur potter, I make my own glazes etc.etc., I can't understand why anyone would want a crazed glaze on a functional item, for me that's a defect, (add some more Silica to cure it).

As to the tint near the edge, it can happen that a glaze on one piece can affect the glaze on another piece during firing, it's known as *flashing*; Cobalt Oxide in any glaze is not really a *flasher*, but it can spit from one pot to another, (but it will be blue), another weird one is if you have any Chrome Oxide, (which makes a very strong green) and Tin Oxide (makes white) in another, this can produce pink, I even have a glaze called Chrome Tin Pink which deliberately makes use of this effect. The colour in your tile is possibly caused by some Iron in the clay, but it could be something completely different, there's so many different things that can happen with chemistry at 1000+ deg C.

Having said all that, I'd be surprised if a commercial manufacturer wasn't aware of those possibilities and took steps to avoid it.

Have you looked at it in different lights and at different angles? I'm just wondering if it's picking up a reflection from the red tiles somehow.

[patmoore]

Thanks ayjay.

I’ve looked at it from every conceivable angle. Definitely not a reflection. More interestingly on some tiles where the colour is, some grout has ‘bled’ in perhaps.

Trying to discern if this is natural or not is so difficult to the untrained eye.

[ayjay]

More interestingly on some tiles where the colour is, some grout has ‘bled’ in perhaps.

Unless it's only earthenware, then that shouldn't be possible if the tile is fully vitrified in the firing.

It's why earthenware (Terracotta) pots will break if kept outdoors in winter, Stoneware will survive (unless it fills with water and then freezes).

Stoneware should have an absorption rate of less then 2% and for porcelain it should be less than 1%.

You can do a simple test for absorption by weighing a piece and then soaking for 24 hours and re-weighing, (I get 1.6% on my stoneware fired at home).

[dewaltdisney]

I have found this very interesting and would offer my own theory based on nothing but guesswork. I was wondering if the crackle glaze provides little canals that allow seep from the grout whilst wet?

DWD