I use bears never had a micro bubble , plastic works good for me.little smokey ....I shake the crap out of it upside down to get all the white off the bottom..i use a butter knife to mix with ..never any wood ..wood has water in it.that little bit with the heat will cause bubbles..or use a tea spoon...I think getting a way from the wood a good mix will fix things for you...also mix after I first heat and all in between.add color last.