Finding the perfect Clear
One of the Holy Grails in Glaze work is finding the perfect clear. The problem to begin with is that there is no consensus on what is the perfect clear. For our studio clear which had to satisfy many people we needed a glaze which was crystal clear; did not craze; left the colors true, by which I mean it did not turn a brown clay grey, change cobalt blue to purple, bleach out iron, etc.
Specialty clears would for example be one that did craze; was a satin matt; had some amount of clouding or streaking, etc.
Many recipes are offered on this subject but it is often the case with glazes that what works for one does not work for another. Temperature and firing schedule come into play. There are some beautiful low expansion clears but they must be fired to ^7. Materials change not only from one batch to the next but from what is available in a given location. What is used in Argentina is not going to be the same as what is used in the northeast of the USA.
If you are going to find what works for you, you need to know what your materials do to a glaze. High Calcium content is going to bleach out iron. I imagine that this is what makes a brown body clay look grey. Boron will cloud a glaze. Manganese will turn cobalt purple. Materials matter.
We can start adding recipes that are favorites and dissecting them if you wish.