cojo Posted August 3 Report Share Posted August 3 (edited) Hey everyone, first time poster, didn't see a previously asked question with this specific issue but redirect me if there was one. I am learning how to make tiles Cuerda Seca style. I apply watered-down underglaze using applicator tip bottles. This almost always produces the following effect: Picture I correct these pinholes as they emerge, but they keep appearing and when the underglaze has settled too much, fixing them results in what I call "scarring" - blemished underglaze surface. This does not happen when the underglaze is painted on I am using BCS-6 and Naranja clays from Clay Art Center in Tacoma, Washington. This happens with either clay body It happens regardless of whether it is bisqueware or green I am using Mayco Fundamentals underglaze, I believe the same issue has happened with Amaco velvet It happens whether I use the metal applicator tip or the plastic tip that comes on the bottles It happens at a variety of water-to-underglaze ratios The water I use has been filtered with a Brita I shake up the water/underglaze mix before applying I have tried dipping the tiles in water before applying the underglaze, and while this may (?) help somewhat, it does not solve the problem It seems to happen more with some colors than others, for example it seems like it happens more with the blue than the green in my picture As you can tell, I've done some testing with this and have been unable to solve it. I have watch videos of people applying underglaze to tile in the same way I am trying, and it does not look like this happens to them. I am rather new to ceramics in general and I don't know why this would be happening. These are the specific applicator tip bottles I use: Amazon.com: Expesumas 6 Pcs Glue Applicator Bottles, 30ml Plastic Squeezable Dropper Bottles with Blunt Needle Tip 14ga 16ga 18ga 20ga for Glue Applications, Paint Quilling Craft and Oil : Arts, Crafts & Sewing Edited August 4 by cojo Quote Link to comment Share on other sites More sharing options...
Roberta12 Posted August 4 Report Share Posted August 4 I looked at the Mayco fundamentals page on their site. The only thing I saw that might apply to your issue is "pooling" https://www.maycocolors.com/color/fired/fundamentals-underglazes/ I looked at your two clay bodies (not familiar with either) and the Naranja has a high shrink rate. And manganese. But the BCS 6 is smoother. Lower shrinkage too. It's rather puzzling. What is your bisque temp? What happens if you put a clear glaze over the bubbles on your underglaze? Does rubbing on the bubbles create the scarring? Do you think it could be too thick? Roberta Quote Link to comment Share on other sites More sharing options...
Roberta12 Posted August 4 Report Share Posted August 4 And.... @cojo Have you contacted Mayco? Their technical people may have some great answers and advice. Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted August 4 Report Share Posted August 4 (edited) 13 hours ago, cojo said: I shake up the water/underglaze mix before applying One thing to try, shaking usually introduces micro bubbles in many thicker mixtures. Sometimes the micro bubbles will coalesce as they rise and form a big bubble or pinhole. Better to stir or gently swirl than to shake most liquids to avoid this. As a solution for when this occurs, Epoxy artists use a very light quick motion with a propane torch to remove their bubbles. Painters often tip their rolled surfaces with a brush to remove their bubbles. Some underglaze observations Too much or too thick of an application of underglaze has its own challenges, can be color dependent, especially if overgrazing. The overglaze may not melt well over a thick layer of underglaze and the pores of the bisque will already be filled so the area with the underglaze will be far less absorbent than the rest of the bisque causing even glaze application difficulties. Final thought Sue McCleod was actually community sourcing many of these issues I believe, hoping to develop a resource for known underglaze issues. You may want to join that effort to some extent or contact her to inquire if it is still ongoing. https://suemcleodceramics.com Edited August 4 by Bill Kielb Roberta12 1 Quote Link to comment Share on other sites More sharing options...
Min Posted August 4 Report Share Posted August 4 Hi @cojo and welcome to the forum. Is BCS-6 the one with sand or without and what cone are you bisque firing to? Quote Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted August 4 Report Share Posted August 4 I haven’t got a lot of experience with underglaze, but the ones I used were Mayco. I found they fired to a pretty soft, smooth surface at cone 6, barring any incompatibilities with other materials. The unglazed surface on some of them hold up pretty well after 4 years in my dishwasher, so I’d call them well melted but very stiff. Not being able to clear bubbles through an application thick enough to be raised tracks with that. I think you may be using the wrong material entirely, and it’s not your technique that’s failing. My understanding of Cuerda Seca is that a glaze is used, as the extra flux is needed to smooth out application marks and leave that slightly raised surface. If we’re sticking with Mayco, Stroke and Coat might be a better product to use, rather than underglaze. Roberta12 and Bill Kielb 2 Quote Link to comment Share on other sites More sharing options...
Roberta12 Posted August 4 Report Share Posted August 4 Also @cojo I have found a couple of potters on Instagram that might be worth a look for you. One is Caleb Zouhary and Renee Lopesti Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted August 5 Report Share Posted August 5 (edited) I think @Calle has the right idea. A quick Wki inquire says glaze divided by a barrier. Wiki has this: Digital fire has flood fill partitioned areas with glaze. Further to Callie’s point, I have painted Mayco stroke and coat glaze colors adjacent and they generally stay separate and do not move. Especially when painted along a carved line. You may be able to emulate just with stroke and coat type products and not need the barriers and flood fill. Stroke and coat is a lowfire glaze that generally can be fired cone 6 and higher and still perform without much movement. This may not answer your pinhole issue, but underglaze does not look like what is typically used for this look. Edited August 5 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
cojo Posted August 6 Author Report Share Posted August 6 (edited) Hey everyone thanks for waiting as I tried some things out - Bill - your suggestions look like they've done it. 1. Stirring not shaking and 2. Applying a less thick coat has gotten rid of the pinholes! Thank you! Quote Is BCS-6 the one with sand or without and what cone are you bisque firing to? Bisque is fired to cone 04 at the studio I go to. I actually had the one clay name wrong actually, it's BC6, not BCS-6 Quote Mayco Stroke and Coat might be a better product to use, rather than underglaze. I initially used Stoke & Coat. I had odd results with it, which in retrospect may have had more to do with how it was fired. Might try it again later - does anyone know if it waters down well? My memory is that it's pretty thick Edited August 6 by cojo Callie Beller Diesel and Bill Kielb 2 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted August 6 Report Share Posted August 6 (edited) 1 hour ago, cojo said: Might try it again later - does anyone know if it waters down well? My memory is that it's pretty thick I have thinned it with water. It’s just a lowfire glaze so I believe you can make adjustments to the rheology as you may be accustomed. When I used it some of the bottles were crazy thick on arrival. Always thought it might be a Qa/Qc thing so I thinned to work best for me. I like my glazes to work without a bunch of effort, there are some here that adjust always or nearly always to their preference. @Hulk I believe has this down pat for himself. Edited August 6 by Bill Kielb Roberta12 1 Quote Link to comment Share on other sites More sharing options...
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