Most old white ironstone I have had was not microwave safe, but every bit has been in the dishwasher countless times..
To test it put a pyrex cup of water in the microwave and the dish you are wondering about....give it 30 seconds and the water should be hot but the empty ironstone dish not hot. If it gets hot, that means the composition of the clay is absorbing the microwaves....and will get very hot!
I did have some old heavy mugs that I routinely heated coffee in and they were fine....and I have a couple of old think they are Meakin soup bowls I use to cook oatmeal in and they are fine also...
So to answer your question...it depends! LOL!
I love old white ironstone!!!
Linda C

I also put my pre-1920 white ironstone in the D/W but not the microwave. I've never tried Linda's test...just figured I'd not take a risk. I use mine all the time 'cause it goes with everything I own except for the fine china stuff. Also, I just like the look & feel.

If you do start collecting...be careful! There's a LOT of post-1970's white ironstone out there mixed in with true old stuff. Nothing wrong with the newer...just don't pay antique prices for it.

Have fun!

Tricia

lindac - Thanks for the microwave test idea. I'm sure ironstone would be fine in the oven, but I do use the microwave for quick reheats, etc.

triciae - I like the look and feel too. I especially love the look of Meakin's Sterling Colonial and want to start a collection! I suppose it's easy to distinguish from the newer stuff b/c of the stamp on the bottom, right?

Real, honest to goodness old ironstone has iron in it. As a result, it shouldn't be used in a microwave - no metal should. I'm not sure if modern ironstone has metal, though.

Lindac do you know if iron slag leaches out of ironstone? i have pontesa the castlian collection

What brand? I suspect that is not really 'old" ironstone....aas in 1900 and before.