Check the china in a very good light and see if there are any hairline cracks in the glaze. Look hard, maybe with a magnifying glass, crazing cracks are difficult to see with the naked eye.

If there are any cracks, tiny or larger, liquid can get under the glaze and cause it to discolor.

DO NOT eat out of dishes if they are cracked/crazed. Germs collect in the cracks.

Beautiful dishes past their prime for eating out of make great decorating items.

My daughter has her grandmother's small size platter she always served southern fried chicken on displayed in her kitchen top of a cabinet with other items. The platter was used to heat food in the oven (not oven proof) and had crazed all over with several dark spots where liquid, etc. seeped under the glaze. It is beautiful decor and a reminder of yesteryear cooks.

Remember, in yesteryear days cooks used crazed dishes and thought nothing about it. They also kept food in a warming oven above the wood stove. No, they did not get sick from the germs because their bodies had adjusted to germs over the years. People of today do not have that built up immunity.

I have some old Ironstone that has dark spots on it. I have heard that peroxide...the strong kind like you buy in beauty supply places...like Sally's...will clean it, but I haven't tried it yet.

Thank you both for your comments. I had looked forward to using this china for a Xmas dinner w/my family since my adult kids remember this from childhood. I am moving w/10 days so will take the time to look harder at this china when I move & get settled. Thank you again.