Despite many years of glazing experience, I always make sure I test any new glazes on the various different clay bodies that I use before I put my faith in a particular clay & glaze combination.
When ordering more of a particular glaze - even if it's from the same supplier - doesn't always mean the glaze recipe is going to be exactly the same and therefore behave in a similar fashion to the glaze you've known and loved. So, again, I usually test a new batch of powder dipping glaze before I commit.
The placement of pieces in the kiln also plays a role. Some glazes react differently depending on whether they are closer to or further away from the kiln elements.
If you're new to dipping glazes, the first thing that will strike you is that most of the time the colour of the glaze mixed up in your bucket looks nothing like the colour you're wanting to see on your pieces. You get used to this :-). For example, Celadon Green looks grey in the bucket but then the oxides and other materials in the glaze mix transform into that beautiful, lush green after they've been heated up in the kiln. Chun Blue looks red in the bucket etc. etc.
Most glazes require dipping twice in order for them to show their true colours. The Sage Green I use quite a lot is brown if dipped once, but then turns into the lovely creamy sage green when dipped twice.
I know that glaze testing seems like a chore ... but it really is worth doing, especially if you use a number of different clay bodies, as these will also react differently with each glaze. So it does pay to test your glazes on test tiles that you can make in whatever shape or size you like, but remember to dip once on one area and twice on another, so you can see the different results. I tend to use underglaze pencils to label the glaze tiles.
These days, the firing ranges provided with glazes (and clays for that matter) are pretty spot on, but again it's always worth testing new clays and glaze combinations before you make your massive tea set and glaze it in a "new and untested" glaze 😉.
Don't forget to stir your glaze in between each dip. Otherwise, the particles in the glaze tend to settle and you won't achieve the desired results.
Also, glazes that haven't been used in a while will tend to settle and solidify in the bottom of the bucket (some more than others depending on their recipe), so always scrape that up off the bottom of the bucket and ensure it is then mixed in thoroughly, as the sludgy stuff contains all the oxides, fluxes, silica etc. that create the colour you're wanting.
Happy Glazing!
Louise
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