if the glaze spots are not too bad, try covering them with silica sand and use the rest of the shelf in firing. after the first glaze firing, the silica sand should sink into the glaze and you can then cover it again with a small amount that will not sink into the melt. kiln wash over all of it and use as normal.
Is silica sand different from regular Lake Michigan beach sand? I have some of that... If it's different, please tell me what to look for as a place like Lowe's...are there different sizes or qualities?
Also, do you mean to do the process of putting the sand on the glaze spots for two separate firings and then putting kiln wash over it, or do you mean firing it just once, followed by a second dose of silica sand with kiln wash immediately over that?
And how does this compare with using alumina hydrate, as the Guinea potter suggested?
I plan to clean off loose kiln wash on one shelf and use it bottom, unused side up in the bottom of the kiln. It was actually 3 shelves damaged, but I bought two new ones. I will be more careful in the future!
Thanks for everyone's help!
Adding this question: Two of the ruined shelves are clean on the other side. I'd like to use one upside down in the bottom of the kiln, of course on 1 inch stilts. I cannot get the glaze spots off and don't want to spend the time and money to get a good tool to do it! Will the glaze spots drip down onto the floor of the kiln if I put that side down?? Here are photos of the spots, if I am able to add photos to this, post. If not, I'll add them in a new post. IMG_4454.JPGIMG_4455.JPG
that's s serviceable shelf grinder from harbor freight $ 20 dust mask eye protection and gloves followed by kiln wash not a big deal