Finishing glaze fired work

[baetheus]

Hello All,

I have a few questions about finishing glaze fired work. In general, I try to do as much finishing at the greenware stage or on the wheel. For my mugs this means:

1. While throwing I compress the base to about 3-4mm thick, wire off with a curly wire to get the final texture, and clean the bottom curve with a wood knife.

2. I use very little water, preferring to use slip from the previous mug while throwing.

3. I finish the rims of the mugs with slippery (covered in slip) shammy leather, mostly smoothing and shaping.

4. While the pots are on the soft side of leatherhard I round off the bottom corners with my thumbs then gently tap in a little dome in the bottom.

However, I have been using Laguna's Death Valley clay https://www.lagunaclay.com/product-page/wc835-death-valley-red which is decently grogged and I've had some feedback that the rims are too rough for some people. Here is a picture of the rims (Personally, I don't mind the roughness and can't feel when drinking from these mugs).

Thus my question: Is there some way during making to reduce the roughness I'm getting in my rim or to smooth it after glaze firing?
 

My other questions are about dealing with glazes that I let get away from me. In my last firing I tried about 50 new glaze combinations and 10 of them came out beautiful but ran onto the shelves. Some drips are quite small:
 

and some are quite large:
 

 

Before now I've primarily been testing single dips of single glazes to keep it simple, and thus haven't run into dripping. I was thinking about picking up one of these diamond sanding discs (https://www.clay-king.com/pottery_tools/diamondcore-tools.html) to clean up what I can, but was wondering if you all had advice for the following:

1. What grit diamond pads would I use for glaze cleanup and polishing to save these pots?

2. How much glaze dripping is possible to correct or worth correcting?

 

Thanks in advance for any advice you can give me and I hope you are all having a wonderful weekend!

[Bill Kielb]

14 minutes ago, baetheus said:

1. What grit diamond pads would I use for glaze cleanup and polishing to save these pots?

2. How much glaze dripping is possible to correct or worth correcting?

 

Just some personal observations
It’s gonna be tough but for large drips and by hand something pretty course may help so 60 - 80 grit likely best to remove significant drips or get them to a point where they can be polished. For polishing all my feet I use 12” 180 grit or higher glued to a batt. My wares are porcelain and have trimmed feet so super smooth is my typical finish.

There is no rule to dipping other than learn by test tile how a glaze responds to your dipping practice. I dip for three seconds, other may dip for longer.  I always make test tiles using one dip, two dips etc…. For each test.

Grogged clay often becomes rough when the grog is exposed during wet finishing. The only way I have been able to get them smoother is to sand after bisque (appropriate dust mask and practices required) using 220 grit paper. As the clay shrinks the grog can poke through so finishing before bisque can raise the grog actually. It’s one of the reasons I pretty much only throw porcelain now.

[baetheus]

@Bill Kielb Thanks for the response. 60-80 grit for big drips and 180+ for finishing bottoms sounds about right. It's really unfortunate that my favorite results tended to be the glazes that got the most movement, but at least it was a mostly successful experiment! As for my dips they are pretty quick in general, definitely 3 seconds or less if I'm going to layer. I didn't mix these particular glazes (they are older recipes from the craft center that I tech at) and they don't have any gravity documentation. It's mostly a go by feel studio so my mileage with technique is going to be varied for the next month unless I take over some of the glaze mixing : /. I'll be honest, I seriously considered trading in this dark groggy clay for a white grogless stoneware because of all the struggle it imparts on making work (best thrown soft, but don't use a lot of throwing water, if you trim you gotta burnish, if your walls aren't just right you'll get some bloat, all your standard glazes get an iron oxide shower, half the glazes wanna crawl, rough bottoms, many people don't like texture, etc etc etc). But after a few days I'm back to looking for solutions! Anyway, thanks again for the response.

[Pres]

You may have to rethink some of your design features of you pots. On uprights like mugs, glasses, pitchers and such maybe a large drip catch at the bottom of the piece would be part of your answer. You may even find that using more of a an unglazed area at the bottom will slow the run of you juicy glazes. The rough clay body should help with some of the running when not coated with a base glaze.

You are definitely in need of a diamond grinding at the bottom to take care of the roughness of the clay body. I would hesitate to push that cup bottom on any finished surface, even the  faux stones so popular in todays kitchens>

 

 

best,

Pres

[Callie Beller Diesel]

A couple of ideas to consider re: the rims:

1) Use a stiff, stable liner glaze that rounds over the lip of the piece. Really fluid glazes are going to break more over that slightly sandy texture.

2) If you want to use the fluid ones, your clay body’s (lack of) absorption appears to be quite good. You could give the finished rims  a light polishing to take off the very high points with 220. 

3) if you want to sand bisque as Bill suggests, do it wet with wet/dry sandpaper from the automotive section. Much better on the lungs and cleanup. 

[Kelly in AK]

Large straight vertical surfaces encourage the glaze to run. I agree with @Pres‘s suggestion to consider design along with finishing methods. The texture of the clay is a feature, quite beautiful, what portion of the bottom can be left unglazed? Can the continuous curve that now goes from rim to foot be disrupted in a way to elevate the pot above the drips, or catch runs in pools? I love the scallop the wire leaves, I’m not encouraging trimming that away. My tool of choice for smoothing out bits that will cut someone is a Dremel with a diamond bit. I dip the part I’m grinding on in water, keeping it wet and rinsed as I go. It works fast. I aim to remove as little material as possible, after realizing how quickly my “touch up” can turn into a scar. 

The running glaze is one problem, the gritty feel another. Sanding at bisque, perhaps. If you address this at leather hard it may save you time. Use a hard tool, like a wooden rib to press the grog back in. Slide a hard tool across areas fingers and lips touch. Wiping, even with thick slip and a smooth chamois, only pulls away the fines and pronounces the grog more. Pressing in is what you need. It’s like what you’re already doing with your finger on the bottoms.

Post glaze fire, say on the rims and handles, a very fine grit wet sandpaper may take the edge off enough without marring the glaze too much. I’m thinking anywhere from 600-1000 grit. You won’t be removing much material, just polishing the edges of the sharpest bits. 

Finally, to a point, there is a place for roughness. Being able to feel the grit is not all bad. Just when it hurts. 

[Pres]

As @Kelly in AKsays the texture is a problem/blessing. I have good luck in heavily grogged clay with a spoon back. A metal one would work like burnishing, and a wooden one would leave more texture. Maybe playing with a variation of both on a piece. 

 

best,

Pres

[Min]

Adding one more suggestion, take some of your claybody and make it into a very thick slip.Add a drop or two of Darvan  to about a cup of the slip then brush it through a 60 mesh sieve. Once the pots are leatherhard brush or dip a thin coating of slip over the rims and base/foot. I would do this after  burnishing the grog back into the clay. Since the slip is the same as the body there won’t be glaze fit or colour issues. The grog free slip will give you a much smoother finish.

Edited October 1, 2023 by Min

[Mark C.]

I would make the lip a bit less sharp as well , Mins suggestion also is good, I think a trim foot / glaze drip catch is also needed. Come 10 work can and will run glaze wise especially when using glaze combos. I have another professional pottery friend that uses the same clay and fires to soft 10 less runs . Thicker lips will help with the sharp edges.

Edited October 4, 2023 by Mark C.

[oldlady]

baetheus, i think you have thought out the really good answer, change the clay.   by the time you do anything extra on a piece you are losing time and money.