technical talk..........

[One Day]

It is caused by temperature differences in cooling.
Best way to illustrate it, samurai swords are curved but the curve is made by painting one side of the steel with clay. Then the steel is heated. It's still straight at this stage. But when the hot steel is immersed in water, the different rate of cooling creates the gentle curve.
So it's down to lazy production really.
Not all porcelain does it, but when it does, it's a pain.
I imagine it matters very little to the factory, but it matters to us!

Incidentally, there's no sand used in porcelain whoever said that?!

 

[GAZ5518]

Good cut Antonio.. You must have used a "Rubi"..!!!
.... Lol
Here we go.....

 

[Qwerty]

Incidentally, there's no sand used in porcelain whoever said that?!

I said that. I have always been told by tile manufacturers that sand mixed with feldspar is used in the manufacturing process of porcelain. I visited the Yorkshire Tile Company years ago and they told me exactly that, and their website still states it....

It's also widely advertised by multinational porcelain manufacturers as in this YouTube video by Everstone (1min 20secs in)....

 

[One Day]

thanks. I learn every day