I purchased two little containers of ITC (one 100 and the other 213) about ten years ago. Used them both at the time, then just the ITC 100 six years ago.
I attempted to use the ITC 100 again last week and it, um, didn't work. I've called a couple ceramic supply places, with mixed answers as to if it has a shelf life, if it's water-soluble.
It's powdered in the container (can't remember if this is how it came or not?). When mixed into a bucket of water, it doesn't dissolve in the least. When it comes from the spray gun, I just get one or two little shots of dry powder (accompanied by a water mist), which temporarily sticks to the brick, then plain misted water.
I'm using the same spray gun I used before, and it appears to not be clogged at all.