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Brief Guide to Glazing
What is glazing?
The process of glazing adds colour and decoration to your masterpieces, and adds a glassy surface which makes them food safe, water resistant and durable.
Glaze is a mixture of powdered compounds (like silica) which form glass in the heat of the kiln (at around 1230 C). It has other materials to make it melt at the right temperature, bond it to the clay and give it colour.
Luckily we don’t have to worry about complex glaze chemistry - we use commercially formulated glazes so they produce consistent results and are safe to use. But you do need to make some choices of how you want your finished piece to look!
Be careful! Glazing is a tricky process!
Block colours, or patterns?
The first decision is do you want to dip your piece to cover it with one, or two, block colours. Or do you want to paint a pattern first, then cover this with a clear glaze?
Block colours are the most common type of glazing for studio ceramics - you will dip your pieces in a bucket of glaze. It produces the most consistent results, and an elegance from simplicity. You really don’t need to over complicate things, especially for your first time glazing. Simplicity will almost certainly give you the best results.
If you want to paint a pattern, you will use underglazes - which are like paints for ceramics. These are just colour - you will then need to dip your piece in a clear glaze for its durable glassy surface.
Painting underglazes is frought with difficulty! The colours come out sort of like they look when you paint them on, but not exactly. You can’t layer lighter colours on top of darker colours. Paint them too thick and the glaze doesn’t stick properly - too thin and they look wishy washy. And remember that you are dealing with a 3D canvas with an inside and outside - so your composition needs to suit the piece you are painting. Many times, students are disappointed with the results when painting.
Block colours are not boring A beautifully shaped piece, or with interest in carving is enhanced with just one colour. A half and half approach, or a splash of another colour can add interest to your piece. These are straightforward to glaze and never disappoint.
Get yourself and your pieces ready
- Wash your hands! You want to make sure you don’t have anything greasy on your hands that might leave greasy fingerprints on your bisc ware. This might stop the glaze sticking and leave a bare patch.
- Dust off your pieces with a damp sponge - to make sure there is nothing which will stop the glaze sticking or leave sharp burrs.
- Wax the bottom of your piece and 4mm up the sides. There can’t be any glaze on the base because it will fuse to the kiln shelf when fired, and will ruin your piece. The wax resists the glaze sticking when we dip. Be careful not to get any wax splashes on your piece - you will be left with a bare spot where there is no glaze. Paint the wax as thin as you can - too thick and it may drip and take ages to dry! (The wax is coloured with blue food colouring so you can see where you’ve painted it - don’t worry it will all burn off in the kiln.)
Prepare the Glaze
Mix your chosen glaze. It is powder suspended in water, and quickly settles. You need to mix thoroughly to get all the good stuff up from the bottom of the bucket. Keep going until there are no thick bits on the spatula.
3 is a Magic Number. Glaze is very annoying stuff. Applied too thicky it will clump on the surface and ruin you piece, or bubble. Applied too thinly the colour will be patchy and won’t give a smooth glassy finish. You need to dip and hold in the glaze for three seconds. Not two, not four, THREE!
Dipping One Colour
If you have chosen one colour, you will hold your piece in tongs and go for a full immersion.
Bisc pieces are very brittle. Hold in the tongs firmly but not with all your might as you risk cracking your masterpiece.
Hold for three seconds, remove from the bucket and immediately turn upside down and shake to get all the drips off.
Be careful not to get an airlock inside (as it will leave gaps in the glaze) - holding so you can see the inside helps avoid this.
Two Colours, different on the inside
Pour the inside colour first, using a jug. As soon as the glaze is at the top tip out with a confident tip! (It will have been at the bottom three seconds by that point.)
Then holding the base in your fingers dip the rim - just near the top, or further down as you would like.
Let this dry a couple of minutes, then holding the top with your fingers, dip the outside in your chosen colour. (Three seconds!)
Warning, to get an exact split of one colour in the inside and one on the outside - i.e. meeting exactly at the top edge - is very very tricky! Try to plan a design that avoids that!
Two Colours, Half and Half
A half and half design is easiest. Hold your piece with your fingers and dip one half, let it dry, then the second half. Do the lighter colour first.
Make sure you look at the inside to make both colours meet - you don't want a gap!
Be careful: when you are doing the second dip you will be touching the glaze. Make sure your fingers are clean - if you have dust from another colour on them you could leave a dirty fingerprint.
Adding Interest
A one colour dip, but will dots or lines where there is no glaze gives an interesting effect ( leaving the raw clay visible underneath). Use sticky tape or sticky dots before you dip in the glaze.
Splashes of a contrast colour (generally over a light base) are fun to do, and give interesting results. Dip in the base colour first, then splash the top colour with your fingers or a paint brush. The colour that works best for this is white, but feel free to experiment!
Choose your pieces carefully. Simple shapes lend themselves to this approach. If you have carving or surface texture adding even more complexity with your glaze can clash!
Finishing Up
To finish. fettle any large drips of glaze with a small blade. Be very careful not to slice back too much, and don’t rub and rub as you will dust all the glaze off the piece. In the kiln, all this dust melts to glass and will flow together.
On the base, and the 4mm up the side, wipe away any small beads of glaze which have stuck on top of your wax with a damp sponge. Any spots left will fuse to the kiln shelf and will ruin your masterpiece! Don’t worry about the wax - this is designed to burn off in the kiln. You must clean your bottoms really well!
Warning!! Hold your piece very gently. You don’t want to knock any glaze, particularly off the rim.
Now your masterpieces are ready to go into the kiln, and a gorgeous finished article will emerge after about 60 hours!