Uneven dipped glaze application

[kayleyvdb]

Hello! I’m wondering if anyone has some tips on getting a smooth glaze application when dipping. Any drips that occur on the outside of my pots while glazing are very visible after firing, even after I’ve waited for the glaze to dry and attempted to scrape off the excess. Any tips? 

[Hulk]

Nice spotty glaze! What is the formulation?

I'm having better dipping results after employing Tony Hansen's suggestions, here https://digitalfire.com/4sight/library/thixotropy_and_how_to_gel_a_ceramic_glaze_73.html

I'm thinning my glazes (I have some white and light blue premix powders, the rest are mixed from raw ingredients in my studio) to ~1.41 to 1.47 specific gravity (I'm keeping notes on each glaze), then adjusting thixotropy with Epsom salts ...then, much easier to apply glaze in even layer, not too thick, and they "gel" (that is, not run and drip!) better.

When piece is lifted out of the glaze bucket, a good grip helps, for a few sharp shakes helps to lose any drips, then wait for the glaze to mostly gel, and finally, smooth any drips with a wet finger before they set up, where the trick is to not smooth too soon, else the glaze will be thin there, and not too late, for the drip won't smooth. Viola! Hope that helps.

[kayleyvdb]

55 minutes ago, Hulk said:

Nice spotty glaze! What is the formulation?

I'm having better dipping results after employing Tony Hansen's suggestions, here https://digitalfire.com/4sight/library/thixotropy_and_how_to_gel_a_ceramic_glaze_73.html

I'm thinning my glazes (I have some white and light blue premix powders, the rest are mixed from raw ingredients in my studio) to ~1.41 to 1.47 specific gravity (I'm keeping notes on each glaze), then adjusting thixotropy with Epsom salts ...then, much easier to apply glaze in even layer, not too thick, and they "gel" (that is, not run and drip!) better.

When piece is lifted out of the glaze bucket, a good grip helps, for a few sharp shakes helps to lose any drips, then wait for the glaze to mostly gel, and finally, smooth any drips with a wet finger before they set up, where the trick is to not smooth too soon, else the glaze will be thin there, and not too late, for the drip won't smooth. Viola! Hope that helps.

Thank you!! Why do you choose to use Epsom salts over vinegar? 
 

The same glaze is used on both of the pieces I shared pictures of, but they are on different clay. The top piece is Plainsman m332 and the bottom is a 50/50 blend of m332 and Laguna’s speckled buff.

The glaze recipe is one I got from a community center I used to take classes at. I had luck with it there so I decided it would be a good recipe to try for my first attempt at mixing my own glaze. 
 

here’s the recipe (the numbers are very specific because I adapted it from a recipe for a large batch)...

36.62 Custer feldspar

15.96 dolomite

15.5 frit 3124

15.96 silica

15.96 kaolin/EPK

2 bentonite

9.39 zircopax 

[Hulk]

Hi Keyley,

Thanks for the recipe - similar to a clear that I'm using (am getting MgO from talc, don't have any dolomite in my materials supply ...yet).

I've used vinegar to adjust thixotropy as well; have used both, just trying both out for fun (looks to me that they both work fine). A few glaze sessions ago, couldn't find the vinegar, dissolved more Epsom salts than I needed, put the cup up on a shelf (labelled!), have been reaching for that since! 

[kayleyvdb]

Okay, good to know!

The bisque I’m glazing is slightly overfired so I was relieved to hear in the video that this technique works on overfired bisque. I gave it a try today with vinegar and following the instructions in the video, but the glaze wouldn’t dry on my pieces. Any idea why that might be and what I can do to remedy it?

[Hulk]

unknown.

I'm adjusting the specific gravity first, then making the addition to adjust thixotropy - doesn't take much to get the glaze to come to a stop faster after mixing, and then bounce back*. I'll add a capful/spoonful at a time in a two gallon bucket (not all the way full - leaving room for glaze to rise when a piece is dipped!).

I'm not recalling the glaze taking longer to dry. What I'm used to seeing is the moisture being absorbed into the clay such that the glaze won't move. This happens quickly, within ten to twenty seconds; the colour and sheen changes as the moisture dissipates, first at the portion that was dipped last, then progressing toward the part that came out of the glaze last (and was also dipped first, eh?). From there, I let all the pieces sit until tomorrow, or, during warm and dry weather, later today - especially if I've carried the ware boards outside to sit in the sun (if there's sun - we get fog too), then glaze the next part. I'll do all the insides, let fully dry, then glaze the outside; if I'm doing multiple outside glazes, there's another wait for the edge to dry... All that to say I'll wait for the partially glazed piece to fully dry before going to the next step, and haven't noticed thixotropy adjusted glaze taking longer to dry. Have noticed that the glaze thickness I want dries faster than too thick tho'!!

*I'm noting the specific gravity in my glaze notebook, as well as how it's working for me - toward any adjustments that may be required next time. Also noting how many clockwise turns the glaze takes before stopping and bouncing back - I shoot for about three to three and a half turns, where the stir speed matches "Rastaman Vibrations" mon. The amount of shear - how together the glaze turns and slows - may be a better indicator. The drippy glaze (low thixotropy) keeps on spinning, and not together, especially as the speed slows down - and no bounce back.

[liambesaw]

you might be fine if you just drop the bentonite from the recipe and carefully dip, holding the piece until the glaze water is absorbed.  I've never had to flocculate a glaze unless it had no clay, yours has 16 kaolin which should be plenty.

Flocculating will increase drying time by quite a bit since the particles are now in a "sponge" formation.  And applying it onto overfired bisque will cause it to take even longer since it wont be able to wick away as much moisture into the clay body.

Try it on a normally bisqued piece and see if it behaves the way you imagined.  If not, careful dipping along with DEflocculation will help the glaze dry fast as you hold it.

Just more things to try!

[Mark C.]

overfired bisqueware will not absorb water fast like bisqueware fire to cone 08 or 06. Its because the body gets less absorbent as it gets fired hotter.

If its really overfired alot it sometime is not worth trying to glaze it.

[Callie Beller Diesel]

The flocculation process does sometimes make the glaze take longer to dry. It’s part of what eliminates the drips, because the wet glaze has a chance to smooth out. 

[Min]

13 hours ago, kayleyvdb said:

The bisque I’m glazing is slightly overfired

How much overfired? Like has been said the less porous the bisque the harder it is to get the glaze to adhere. Try warming up the bisque to around 200F then glazing, I'ld be hesitant to mess with a bucket of glaze for a few overfired bisqued pots. Have you measured the specific gravity of the glaze? Could just have too much water in it.

[kayleyvdb]

1 hour ago, Min said:

How much overfired? Like has been said the less porous the bisque the harder it is to get the glaze to adhere. Try warming up the bisque to around 200F then glazing, I'ld be hesitant to mess with a bucket of glaze for a few overfired bisqued pots. Have you measured the specific gravity of the glaze? Could just have too much water in it.

I’m not sure exactly how overtired they are, unfortunately. I expect they are fired to a cone 04 or 03. I didn’t realize they were overfired And ran two firings... so it’s two full kilns worth of work that I’m supposed to deliver to a boutique, which is why I’m trying to find a solution! I may just have to remake everything though.  

The glaze recipe I used doesn’t share the ideal specific gravity but my glaze mixture is 1.46. I have been heating my work in the oven first!

[Mark C.]

The best you can do is warm the ware and hold it uner the galze a bit longer and wait for it to dry (takes a while longer) after dry scratch test for thickness .

[Min]

1.46 should be in the ballpark and ^04 bisque should be fine too, it's what many people bisque fire to. This is going to sound silly but take something that you know you haven't overfired in the bisque and touch the tip of your tongue to it. Now take one of the pots from the overfired load and do the same thing. The bisque should grab onto your tongue a little bit, compare the two. See if the overfired stuff grabs your tongue, it will if you went to ^04. If it doesn't maybe think about remaking the pots.

[kayleyvdb]

21 hours ago, Min said:

1.46 should be in the ballpark and ^04 bisque should be fine too, it's what many people bisque fire to. This is going to sound silly but take something that you know you haven't overfired in the bisque and touch the tip of your tongue to it. Now take one of the pots from the overfired load and do the same thing. The bisque should grab onto your tongue a little bit, compare the two. See if the overfired stuff grabs your tongue, it will if you went to ^04. If it doesn't maybe think about remaking the pots.

Good news - It sticks! Thanks for the tip. 

[kayleyvdb]

On 8/27/2020 at 7:30 AM, Callie Beller Diesel said:

The flocculation process does sometimes make the glaze take longer to dry. It’s part of what eliminates the drips, because the wet glaze has a chance to smooth out. 

Thank you, Callie! Quick question: I typically like to do two coats of this glaze. Do you think that will be necessary when it's flocculated? It appears to be going on more thickly than before flocculation, and it's the second coat that's taking ages to dry...

[Callie Beller Diesel]

@kayleyvdb 

Yes, flocculation will make a glaze go on a bit thicker. 

Typically if you're dipping a piece and only using a single glaze, you're doing it because you want to apply a layer of glaze quickly and efficiently. While there are a couple of specialty glazes that require a very thick application to get specific results, they tend to be the exception rather than the rule. I'm not sure why you'd dip this particular recipe twice, unless you're used to doing that because of the way this glaze was mixed in your group studio. Keep in mind specific gravity is a very personal measurement: So much of it depends on your clay's porosity that will vary with different clay bodies and different bisque schedules, your water,  how you prefer the glaze to look, your dipping technique and a host of other things. It's a number you decide for yourself, which is why sg numbers aren't always handed out with glazes, and when they are, they're a very specific snapshot of how the artist who provided them works. 

If you really want to understand flocculation in glazes, I can't recommend Sue McLeod's blog and facebook group enough. She is the delightful combination of a technically minded person who is also a very good teacher.

edited to add: I just wanted to mention too, that you don't have to quote the folks you're trying to get clarification from, or someone you're trying to get the attention of. You can just tag them by typing the @ and beginning to type the person's screen name. Select the right one from the dropdown that appears, and it'll appear highlighted in green like here. The tagged person will get a notification when they next check the forum.

 

[kayleyvdb]

@Callie Beller Diesel - Thanks for the tagging tip! This is much easier.

The reason I want to double dip this glaze is to get a layered look, and this method has worked well for me in the past... But rather than doing two separate dips, I wonder if I could do a quick dip for the entire piece, then hold it a bit longer in the glaze on the areas I want to be more opaque. What method would be best if I wanted to layer two different glazes? Perhaps using a flocculated glaze wouldn't work for this?

I didn't realize Sue McLeod had a facebook group. Thanks so much! Joining now...

[Callie Beller Diesel]

2 minutes ago, kayleyvdb said:

Perhaps using a flocculated glaze wouldn't work for this?

It's possible. Without having worked with it personally I'd have said that, just going by the recipe, there's enough clay to keep it suspended adequately without it. Also, I find that frit 3134 is somewhat soluble, which would also assist with keeping the glaze from sinking too quickly. 

Flocculation and deflocculation are handy tools in your box, but you don't need a screwdriver for every single job.