Anyone used Giotto Decopens for porcelain painting?

It says you can and shows a picture of painting mugs with them, I want to do this for father's day, does anyone know if they are washproof, or have to be sealed or anything?

Thanks in advance! :)

We've just done these this afternoon, they look really good, not sure yet if they can be washed, I'll check later and let u know:o

I've got a feeling the pens are only permanent on porous surfaces, not glazed or smooth things. I tend to use the Giotto pens on srones, salt dough shapes etc.

For porcelain I use these, which can be heat fixed:

http://www.bakerross.co.uk/product-Pearlised-Glitter-Porcelain-and-Glass-Paint-Pens-EV652.htm

I've never used them but it says they are water based which implies to me the colour will wash off.

Miffy xx

They wash off the mugs we did it!

Not looking good then, but thanks for the replies.
I have just seen some on Baker Ross that are reduced, might have to order some and hope they come before Friday!

(proper porcelain ones I meant to say)