Ben xyz

Tried looking for the answer to this one without luck (though it's likely here somewhere). Apologies in advance if repeated: An underglaze color is applied to greenware and fired to c04 (bisque). If, for any reason, it is fired again at c04, will the underglaze shift in color from the first low firing to the second? (I am aware of color changes from low to midfiring and above).

Since I've learned here that Palladium will oxidize over time (due to its manganese content), I'm wondering if there's a way to stop it or slow it down with a sealer of some kind? Not sure if it's a result of exposure to oxygen or it's something inherent in the material itself; or perhaps a result from handling? I have a (decorative) plate trimmed with Palladium and would prefer it not to tarnish and darken over time. Also wondering if that happens with metallic lustres as well?

Thanks Min for the link. Nichols did say: "After firing, I coat the underglaze surface with a food-safe oil sealant (like Salad Bowl Finish, available from home centers) and wax used by woodworkers. This seals the outside surface and makes it fairly durable, but check the instructions on the containers for care and use of these products." Doesn't seem like it would be a very durable surface for something that holds heat, like a teapot, but it seems to work for him. "Fairly" might be the key word there. I would guess the underglaze color would change/deepen with the application of anything oil-based (which may be desired). A UV blocking spray might be helpful for non-utilitarian objects, if it's permanent. I may still contact Nichols about his ongoing experiences with underglazes, since Amaco does not fully know about their products. Likely having a clear glaze coating would legally leave them off the hook for any food safety issues and possible leaching chemicals.

Having the same problem with large 14"x20" slab(s), 3/8" thick. I am using recycled studio clay (medium and hi-fire clays mixed together), rotating and flipping the slab often when using the roller (16lbs at a time before trimming). Compressing after with metal rib for further compression before drying. It only occurs when glaze firing (c5) stage and not on bisqued slab (c04). 1. Also making grooves on the back to counter warping (see photo). Perhaps this is making thinner areas against thicker and causing the cracking in half? 2. How do "waster slabs" work? Slightly larger and thicker than initial slab? Placed under bisqued slab? Or under greenware from the beginning? A new process for me. 3. Since these slabs exist as elements in a sculptural piece, I 'm now tempted to glaze fire at a bisque temperature (c04), using a low-fire clear gloss glaze over the underglazed slab and calling it a day. Not as sturdy (w/o full vitrification), but wasting a lot of time, energy and clay from these large slabs cracking in half at c5. Thoughts?

Thanks for link. I agree with you, Min - thought it odd as well. Why use the description 'velvet' when it can't really be used in that form? Being the priciest of underglazes, I had hoped they would have better customer support. It's possible that the answer is 'not archival', but they didn't want to say. According to Amaco, they didn't bother testing them out in their velvet form, because they're intended to be only under another glaze, end of story.

Any ideas on how on re-create Bertoncello's glaze from the 60's/70's? There was an Antique White (c5) at the studio for a while which was similar, but too expensive for them to continue making. Thanks! Note: Have also posted this question on Glazy as well. Will relay any info possibly found there.

Thanks for suggestions! May go in w/ a couple buddies for this product: https://madeofaustralia.com/liquid-quartz/ It is a food safe, permeating sealer designed for use on unglazed ceramic ware, rendering it waterproof, stain resistant, & yet completely unchanged in appearance. Liquid Quartz can be applied to all unglazed, stable, porous surfaces; bisque ware, vitrified ceramic ware (yes it is still porous) & alternatively fired clay bodies (pit, smoke, saggar, barrel, naked raku) to create an invisible, long lasting, protective barrier against moisture, food juices, & other contaminants. Made from SiO2 (or Silicon Dioxide/Silica), a naturally occurring oxide & one of the most abundant minerals found in the Earth’s crust, most commonly in the form of Quartz. It is used extensively in the production of glass, glazes, underglazes, clay body stains as well as terracotta, earthenware, stoneware & porcelain clays. It is highly abrasion resistant (7 on the Mohs scale) & thermal shock absorbing.

Have recently been working with Amaco's velvet underglazes, with clear gloss over some areas of decorative plates and other areas left matte (cone 5). Amaco had previously informed me that they had not done any tests with their velvet underglazes if left matte/velvet and could not vouch for the velvet finish being archival. These are purely decorative plates btw, not used with food. There appears to be only one glaze (out of Australia) that can be used as a matte sealer which does not visually alter the original surface. Unfortunately, it's only sold in large quantities and quite expensive to ship. Thankfully a spray booth has recently been set up at the studio, which will enable me to try out clear matte/velvet glazes, with as few coats as necessary, since they usually become cloudy and lighten the underglaze colors they're applied over. Any success with clear matte glazes (without fogging) at cone 5? Would like them to become archival. Thanks! Attached below: Circle designs have clear gloss glaze over them, with velvet matte surface on the rest.

Thanks! I always try to remember to rotate and flip the clay when rolling through the device with its thickness increments (but good to be reminded of). Pressure from as many directions and angles appears to be the key. Pounding the clay first makes sense, which I'll try. The 'memory' of a clay's previous bending is a reality. Will avoid it when transporting the slab to work station after rolling. Will look in the silicon sand, too. Probably trying different clays might help (some more warp-able than others). Appreciate all the suggestions.

Attempting to create and fire a flat ceramic plank (unglazed) say 12" x 18" x 1/2" thick, to use in a sculpture (dimensions are somewhat variable at this point). The issue I have is warping. I've heard of placing a weighted bag (rice or sand) on top of it, or perhaps a flat board on top while it dries. The warping in firing is the next issue. Lying horizontally flat on a shelf is one option for (cone 5). It will pick up kiln wash, but may have to live with that. Another option is creating a clay box with slots (to minimize wrarping) to hold the plank on its side. It will not be glazed, so running is not an issue. Type of clay may help, too. Ideas? Thanks!

Thanks for the responses! I figure I will likely treat this first re-glaze effort purely as an experiment. Maybe try the underglaze on top, bisque fire (for better adherence?); then satin clear at cone 5. Will later repeat building the same form, but with the revised glaze choices I feel good about. Interesting term "eutectic" btw...have something to perhaps stump the glaze teacher with.

Because of some detailed stamping on a hand-built piece, I thought I might use the atomizer with clear glaze/cone 5 on two fairly flat surfaces (trying to avoid small glaze bubbles from forming if dipped). Curious about how many coats I should I expect to spray on with this device - experience? Thanks!

In an attempt to salvage, I was thinking of covering a previously fired piece (at cone 5 / matte glaze) with a white Underglaze as a kind of primer, before glazing and firing again. Tried it? I know re-glazing a fired piece is a hit-and-miss proposition at best. There's also the possibility of bisque firing this pre-primed object before applying another glaze and firing c5. Had also heard about heating a surface somewhat (w/ heat gun) and then spraying on a glaze for better adhesion to a previously glazed/fired piece. Any luck?

Thanks Mark - Laguna retail is near here in LA (will give it a go). No need for snow tires ;-) Nope Betty, not giving up quite yet (thanks!)

Tried using this as my first foray into latex resist. Wanted to warn others about this particular product, which ended up leaving a nasty residue on edges, after mid-fire (see around outside of checkerboard circle). Textured too! I thought I totally removed it all before firing - weird hard glossiness as well. Perhaps will try to somehow sand it off. Bummed. Will try another brand in the future.