Cynthia sounds to me like it is time to get a lathe so you can try some of these things.
On goblets I finish the insides of mine with a epoxy finish. It makes it pretty stable and have never had one crack. As far as bowls, vases, etc if they are turned correctly, dried properly then there is not much of a problem with cracking. I have several vases that are 5 or more years old and none have cracked. We are in a dry climate (read summer around 10% to 15% humidity). I have several bowls we use for cereal and soup that we use at least 5 days a week and no cracks. We have plates and salad bowls we use several times a week that are 3 to 4 yrs old that we use several times a week with no cracks.
Retirement: That’s when you return from work one day
and say, “Hi, Honey, I’m home – forever.”
To succeed in life, you need three things: a wishbone, a backbone and a funnybone.