I fire them to cone 11 and my porcelain feet stick if not washed.
There are many ways to do this but this is what I have been doing for many years as far as washing shelves.
This will work with all types of shelves-advancers -mullite- corelite-dry pressed English-silicone carbide-whatever
There are many ways to apply wash brush -spray -roller. I like a heavy nap paint roller that leaves a nice stipple texture.
We are losing our heat with the sun getting lower and this job is easier if its sunny and warm .So today was sunny and warm so I did a dozen to get warmed up for big job in am.
First I grind the backs where any posts have left anything sticking up (yes I was my post tops and bottoms)
Then I flip the shelve and grind any rough or glazed areas and make them smooth. One can use a grinder-a carbide brick rasp-whatever. I choose to use a 4-inch Makita and a 7-inch Milwaukee sander with variable speeds.
I like to lay them out on ladders or anything waist high.
Get out your safety gea ras seen in photo-hard hat is handy for bear attacks as well and will protect you from falling tress and meteorites from space. Use the safety glasses andear muffs at least-keep lose clothing tucked in and read all the small print till you snap or go insane-do not wear a tie while grinding. Bow ties are ok.
I use an old bath mattor carpet or piece of rubber as a pad-make sure this cannot get into grinder.
If a grinder is too dangerous for you use masonry rubbing stone instead.
After grinding I lay them on a ladder and brush them off to remove the dust. Then let them heat up in sun.
I mix the wash like heavy cream and use a 5-gallon roller screen to remove excess wash from roller.
I roll on one thin coat and let dry in sun. Then when dry apply another really thin coat.
When dry I scrap the edges down with old knife but any tool will do. The wash tends to roll over the edges when applying and is an easy scrape at this point.
Then I stand the shelves on end wash-to-wash sides and when ready to load bisque fire I bisque them before glaze firing. With advancers you must go real slow as the wash got them wet and they need to dry slow other wise they can blow up. Never had this happen but know of it happing. Other shelves are less prone to this.
Here is the process in photos.