Post 33 Glaze application

You'd have to agree that a bonsai pot that's 350 to 400mm long is not something that you would ever think about glaze 'dipping'. Just imagine the volume of glaze you'd need, let alone begin to think about keeping the glaze off the base and inside surfaces.

The only two practical options are spraying and brushing.

I like the idea of spraying to get an even smooth surface but you do need a ventilated booth to do this best. There is a lot of glaze wasted too, which I don't like, and then more importantly how do you know when you'ge got enough glaze on the pot?

So it's brushing for me.
That still leaves the probelm of how much to put on and how to get a smooth application.
I read up on glaze SG to get the right composition for brushing etc etc but HOW MUCH DO YOU PUT ON #@$@$??? Obviously you work it out by trial and error until experience becomes intuition and you just know. Well that's all very well but as with most things I'll be convinced when you "show me the numbers". Getting the data sorted also offes a level of repeatability. There's nothing quite like having a reliable rule of thumb to apply.

I know from my test tiles how many 'coats' to put on and when I do the same on the pots I have begun to know how much I have applied for that number of coats. For the pots I've glazed recently I've nearly applied around 100gms of equivalent dry glaze material. That is I mixed up 100 gms of dry components to make a batch and nearly applied it all to the pot. Taking some measurements on the pots to work out the surface area over which the glaze has been applied reveals an application rate of about 600 to 650 gms of dry glaze to each square meter of surface. I haven't been able to find any similar advice or benchmark in anything I've read anywhere on the internet. So work out the area to be glazed, multiply by 600 to 650, make a batch with that much dry materials and then put it all on the pot. Problem 1 solved. Some glazes do need a heavier application than others and so I'm afraid trial and error and careful observation will tell you which is which.

If anyone has their own rules of thumb about glaze application I'd love to hear from you and will publish the results. There are a lot of folks who are interested in and looking for reliable glaze recipes. That will take you a long way but you still have to get the application right too.

If brushing is the answer then Problem 2 is about which brush to use.

All the advice available says to use a really soft brush, fill it up with glaze and slap it on. The topmost brush in the photo is the usual sort of brush available for the purpose in the pottery supplies shops. Yes the bisque does suck the glaze onto the surface, particularly for the first coat, but what a heavily laden soft brush does, because it can't actually move the glaze over the surface, is deposit a very uneven glaze depth, which on firing translates to a bump in the surface each time you hit the pot with a new brushfull. Very unattractive.

My next trial was a high quality sable artist brush called a mop. Slightly more controllabe and nice to use but generally the same result.
This took me right back to when I started and was just 'having a go' using a regular domestic paint brush for acrilic paint - a synthetic one with standard firm bristles. Because it is firm you can spread the glaze and get a smooth application at all the junctions between wet and dry, glazed and not.
If you are just trying to work on the basis of a number of coats, then with a firm brush how many do you apply?
Well the answer is that if you know how much glaze you need to put on the pot (probelm 1 solved above) the number of coats is academic - just keep putting on thin layers and get the best surface finish!

Finally I have found that a final burnish with a finger or soft piece of cotton fabric will remove any residual brush marks.

So my new rule of thumb is 600 to 650 gms/square meter and a firm brush to apply the full glaze batch is the summary of my limited but tested experience -  for now! What's yours?