i dont think there is anything you can apply to them now, as they have already been fired. it seems to me that anything you put on them now would be even more likely to leech into food than the glaze.

there are tests available to check the existing glaze for food safeness, but i'm not sure where you get them. you could try doing a web search.

To be on the safe side you could always use them to serve things like potato chips, crackers, nuts etc. I wouldn't use them for a snack mix with fruit to be on the safe side. Anthing without moisture or liquid in it can't leach out the lead if there is any.

I lived in Venneauela and the clay I used came directly from the local river and I know that there had to be lots of unsafe chemicals in it.

Thanks for taking the time to post. I did have a lead test done and they are really full of it. So, sadly, I think they will have to be decorative only. But, thanks anyway. Mary

Mary-
You're doing the smart thing. I used to work for the Environmental Protection Agency in their Lead program. One couple I dealt with had brought back some beautiful dinnerware from Mexico, and started to get sick several months later. Their condition and symptoms got so bad they had to be hospitalized; the doctors finally figured out that they had lead poisoning, which came, of course, from the lead that had leached out into their food and drink. They had to undergo chelation therapy to try to reverse the effects.

We knew about this back in Tucson Az 50 years ago. Friends would bring back great pottery from Mexicao but we couldn't use it because of the lead. I think we put some glass plates over them so the designs would show thru.
I'm wondering if you couldn't put some of that saran type stuff on them and pull it around to the back so the surface is showing but of course the food or snacks would be on the plastic. Just a thought.