Wednesday, 12 January 2011

Glazing and stuff.

 Ron asked about what glaze I am using.  It's a simple one - 8 parts lead bisilicate, 1 part flint and 1 part clay.  To get a honey glaze I add some iron oxide and a proportion (random) of the clay element is the body clay.  But, in order to bulk it out, I try and use a fair bit of hyplas as I've found the glaze a bit runny otherwise.  The recipe ingredients are what I had to hand and matched Mary Wandrausch's glaze, but the proportions are, i think, those of Paul Young's glaze (taken from the slipware book.)  I like simple glaze recipes like that.

Here's a first stab from last year:


As you can see, the glaze is quite rich but full of little blisters.  I quite liked the result except for the blisters, but I do know that it got quite hot, but how hot I don't know.  I didn't have any cones other than cone 1 and that went completely flat.

I thought I'd try again, anyway, but I bought some more cones.  Here's the result.


This time, I got cone 1 to go over perfectly (or was it 01?)  But still, blisters.  Far fewer blisters though.  And the glaze isn't as rich, although it was a remixed batch.  I don't like this nearly as much.  My only resort now is to mix another batch and fire even lower - cone 01 or cone 02.  I bisqued quite highly too, but I don't think I'll do that again - over 1000 degrees before, but I think I'll stick to my usual 980 or so this time.

I am dipping the glaze on to the pots, and I'm wondering whether to use a brush instead.  Thoughts?  I know I can get nearer the foot that way.

On that second batch of mugs and beakers I tried a black slip, without success.  As you can see it's just brown:


I think I might add some colour by mixing a clear version of the glaze and adding some oxides - small amounts of copper and cobalt should do for some colourful splashes and dots.

Another thing I did was to glaze all over, and use stilts in the kiln.  I like this, but the stilts I bought were far too small, so on my second attempt, a load of pots just fell over (the cats jump up on the kiln to keep warm.) I won't do that this time, but wondering whether the pots need wadding or not.  Do they?


Anyway, I'm no where near firing anything yet - it's so cold here, all the pots are in the house, but still they don't dry out.

Anyone any thoughts on what I've said?

11 comments:

  1. Hey, not a bad start there!
    In my experience this low fire stuff has little room for error in the firing. So getting the temps right is important. Cones are a must. Not sure about the bubbles but I think you should get a few different clear glazes and test each one and see what works best. PY's and MW's are good to start and I bet Hannah would give you her recipe.

    I know you are a bit adventurous in your glaze mixing sometimes :0) Well, cut it out. Ha. If you want good results (in four weeks time) then we need precision!

    Good idea about adding oxides to the clear glaze. Another solution for color would be to add oxides to your white slip. I have found that I can rely on my slip much more than I can my glaze. So I am thinking of using slip for color instead of glaze. Plus if you do some slip dots etc you can scratch through them if you want to add another layer of depth.

    I don't worry about glazing the feet. My clay vitrifies pretty good at cone 04. I think Hannah uses stilts, not sure about PY. Or you could glaze the bottoms and wipe it away. That may help seal the bottoms a bit, but not stick it to the shelf. (not really sure about that).

    Whew, that's a long comment. Sorry.

    ReplyDelete
  2. Black.
    I'm using Clive's black slip.
    Red Clay 8
    Red Iron oxide 1
    Manganese dioxide 1

    Also someone recently told me this combination of oxides (below) gives a true black. She adds it to base glaze or white slip base. I haven't tested it.

    Cobalt (not sure if oxide or carb) 1%
    Iron Chromate 8%
    Manganese dioxide 6%

    Just something to have in your notes for future testing maybe.

    ReplyDelete
  3. Thanks Ron - useful as ever. Yes, i am a bit 'adventurous' with glaze mixing - but I am learning. I shall mix a few tests and see what comes of it. PY's glaze uses feldspar instead of flint - will mix some small batches to try out. Pretty much stuck with lead bisilicate at the moment - no time or money to get anything different.

    Will try the slip thing too. My thinking at the moment is something along the lines of the Jim Malone pots I have/had, which have small splashes of colourful glaze over the top of a clear glaze and slip. Of course, he's added a brush deco which I can't do, but I want to try some hakame and such on earthenware.

    I guess I'm kind of aware that there are a few folks doing earthenware over here - Doug, Matt, Hannah - I don't want to look like I'm just copying what they're doing (although in reality, that's kind of what i am doing.)

    ReplyDelete
  4. I think the bisilicate or sesquisilicate is the way to go. (I couldn't do it over here but it seems accepted there).

    You are in the land of earthenware (and Leach-ware) so I don't think anyone can fault you if things overlap a bit. I know I've gone through several stages of deco over the past few years in this earthenware line. Most important is just to get some things done. Of course I don't think Hannah has anything to worry about, she's got the trailing skills!!!

    I'm off to slip some cups now. Cheers, Ron

    ReplyDelete
  5. To be honest, I don't think any of them - Matt, Doug, the Pauls - have anything to worry about. This is mostly about doing something I like but which I hope will make money. It was Matt B's idea really - he's been talking for ages about doing something other than the wood fired work - more bread and butter. However, I'm not treating this as any easier than the wood fired stuff - I can certainly attest to the fact that it isn't.

    Are you not allowed to use the lead glazes over there? Would that mean I wouldn't be able to sell my pots to/in the US? Not that I'm thinking of it, just want to know.

    ReplyDelete
  6. Any type of lead in a glaze is frowned upon here. Fritted or not. I don't think it's illegal but it'd be a tough sell to the general public. People ask me at shows all the time if I have lead in my glazes. It's just not done here.

    Good idea about the bread and butter pots. It's hard enough selling any pottery these days. I'm trying to do what feels right for me but at the same time I'm making pots that are a bit more accessible to the public.

    ReplyDelete
  7. I think they're lovely Andy and I think it's great that you're making earthenware pots. I remember you making some really nice ones at my place a couple of years ago. I use LBS 80 Clay 20 - red clay for honey, Hyplas for pale yellow - and recently a blend of the two, 10 red clay, 10 Hyplas.

    I fire bisc to 900 and glaze in the wood kiln to 03, although I have fired it to 01 in the hotspots, but it makes the galena go very dark. I fire to 1080 if I glaze in the electric.

    I do occasionally fire on stilts, but by and large I like to see a bit of the clay body. Great stuff and fab to see you back on the blog. Do you think you'll try earthenware in the wood kiln?

    ReplyDelete
  8. Thanks both.

    I don't quite understand the lead thing - I think even in medieval times most of the lead problems came for potters, didn't it - not the people using the pots, necessarily. And modern lead frit is quite safe - no worse than lead crystal, is it?

    Doug - I have those pots sitting here - the tankard and a yunomi I made - really nice. Alas, I am not planning to wood fire these pots -the idea is to make this easier - cheaper pots, more of them. I hope to do some wood firing again - perhaps in the summer. It's just too hard on your own, though, and so expensive, it isn't really worth it.

    Will try my glaze without the flint. Good idea. Funny, I have several of your pots that are quite dark - red almost - lovely lovely (that jug with the copper blown on to it - would love to get that kind of finish.) Oh well - will make some tests tomorrow to fire early next week with a mix of glazes, and see which is best.

    ReplyDelete
  9. I think if the pots are fired properly and the glaze formulated properly then it's safe. There's really no way to tell unless you send your pots off to have them tested for lead release. I've heard that some commercial dinnerware makers/companies use lead fritted glazes, but of course they have a Quality Control lab right there on premises. For most potters it's not worth it and with new materials out then lead has gone the byway. In this country at least.

    Of course I agree that lead glazes are beautiful and certainly there is no other way to achieve them.

    For me it's not worth the risk...AND you certainly can't convince the general American public to buy a lead glazed pot. Not one for everyday use, they just won't do it.

    ReplyDelete
  10. Hey Andy,
    That Ron bloke is good isn't he. I wonder if he could send some of that sage advice my way. I could do with a proper crit,
    He's right with the glaze thing I feel. Doug seems to get away with being slightly less accurate than me but the lead thing is about the glaze having melted properly I believe. You can have it tested, not sure what the English law is but in Scotland you HAVE to have it tested. It's bloody expensive though, about £75 per piece the last time I did it and you're supposed to have an open and a closed form done and in every glaze you use etc etc.
    Those beakers are lovely, I'm thrilled you're making pots again and of course slipware is the way forward. Don't worry about "copying", you will make it your own I am sure and I think you will always be honest about what you are doing anyway. It has the lovely fabulous history so why not celebrate that tradition and lovliness.
    75% lead 25% red clay by the way, depends a wee bit on your clay though but pretty much somewhere between that and 70:30 should give a good honey. I'm just testing some more at the moment but I'm a bit wary because I should have it tested, hmmm £££s.
    Stilts I use sometimes and not others. Some pots are turned some not. I use the stilts and glaze the bottom probably mainly as an aestheitc thing rather than to make the watertightness. The glaze should do that on the inside.
    Phew, just shout Andy if you need anything, I may not necessarily be able to help but I'd do what I can for you, you've got my number.
    Keep at it chuck, 4 weeks is a stretch but hey nothing like a bit of pressure!
    hx

    ReplyDelete
  11. Good to hear what Hannah says about the glaze issue and it having to be tested in Scotland. I think that's good practice.

    ReplyDelete