Techno Tip: Passing Gas Gassing: it’s unpleasant and you don’t want to do 1t in public. Well, we all have it and it’s all natural! Still, not a good thing to have, especially when it’s trapped and then released at inopportune times. It can be very bad and even embarassing... for your pots and glazes. Gas is the cause of those dreaded bubbles, pin holes and blisters, from tiny ones to big craters. All glazes have bubbles but it’s the larger ones near the surface that create all the defects. All this gas comes from: * Air trapped in the clay body or glaze layer * A by-product (1.e..water vapor, carbonates) from the heating of the clay body or glaze layer ingredients It would not be a problem if all this gas just escaped nicely, quietly and left a nice fresh scent. The thing that gets in the way is the melting of the glaze. Once a glaze starts to melt, turn fluid and seal over, that’s when the gases can no longer quietly escape. Instead, the gases are trapped and turn into bubbles. I often watch my oatmeal bubble and that’s what I imagine happening to the glaze on a pot. Oatmeal is pretty gooey or viscous, but glazes are even more gooey, so the bubbles rise through a glaze very slowly. The smaller the bubbles, the slower they rise or not at all. Then when the bubble makes it to the surface, 1t has to burst and heal over. So can you get a prescription that cures gas? Just as the doctor says... well... some remedies work for some types. We can reduce the gas production, help the gas and bubbles escape and help bubbles burst and heal over quicker . This is much easier to do with cone 10 type glazes, but some minor changes can affect lower temperature glazes as well. Use of a glaze calculation program can help too. In general, these are some of the things you can look for or try to change: * Reducing the gas-producing ingredients in the clay body. This is difficult unless you mix your own clay body. Select a porcelain or smooth white clay over the darker more grogged bodies. * Reducing the gas producing ingredients in the glaze Replace carbonates like whiting (Calctum Carbonate) with wollastonite. * Replace talc with dolomite and barium/strontium carbonates with frits (The glaze calc programs come in handy here) * Raising the melting, sealing temperature of the glaze (closer to the maturity temperature.) * Replace alkalis (Sodium, Lithium and Potassium), nepheline syenite and boron (gerstley borate) with other higher temperature fluxes like calctum, magnestum and zinc. * Reducing the surface tension and viscosity (gooeyness) of the glaze allows the bubbles to burst and heal overt easier. * Look for or make an addition of zinc oxide and/or magnesium oxide in the glaze. Note, a little zinc is great, but too much and you get different problems. * Making the bubbles join together into bigger bubbles so they can rise through the glaze faster Look for or make an addition of zinc oxide in the glaze. A thinner layer of glaze will be easier to rise through, so try not to apply too thick a glaze layer. ¢ Allow time for the gas to escape as well as the bubbles to rise, burst and the glaze to heal over. Fire slower until you reach 1000 degrees C. Then hold the kiln temperature at a slightly lower temperature after reaching peak temperature. If you wanted to be a rebel and take a different approach, you can create a glaze that is very viscous and gooey that will not permit the gases to bubble up and escape at all. The result is a lot of trapped tmy bubbles in the glaze. If it’s a clear glaze, it will have a cloudiness to tt and if you look closely, it’s because there are tons of tiny bubbles in the glaze. The surface is still nice and smooth in most cases. Glazes with lots of boron or gerstley borate are like this. Itll be super stiff... never runs off a pot but itll have lots of tiny bubbles. I hope these tips point you in the nght direction so you can do more research and/ or testing to help relieve your trapped gaseous condition so you can go about without worry of embarrassment... about your glazes. ’m still working on mine.@ Don Jung EEE