roderick

.....another link for Tom http://www.airihortling.fi/Lead release in glazes.pdf

Thank you everyone for your replies, especially Tom. So I have a bucket of dried clay that I found in the shed. It has been frozen and thawed and frozen again for a number of years and is now in a dry and flaky state. I have some Hyplas 71 Ball Clay but as I am more one for street terms I don’t really understand the chemistry of it all :o) I guess this will be OK to use... From Digital Fire Devon medium strength low iron ball clay Oxide Analysis Formula CaO 0.10% 0.010 MgO 0.30% 0.040 K2O 1.80% 0.104 Na2O 0.30% 0.026 TiO2 1.60% 0.109 Al2O3 18.75% 1.000 SiO2 70.50% 6.381 Fe2O3 0.80% 0.027 C 0.20 LOI 5.30 Oxide Weight 512.18 Formula Weight 541.99 How important do you think it is to sieve the dry clay once I have crushed it a bit? It was a pretty clean slip until it got frozen and left. Tom, this you may find interesting. Goes a bit over my head... http://www.airihortling.fi/The%20color%20changes%20with%20earthenware.pdf ...and an online version without the photos? http://www.uiah.fi/kll/hortling.html ...and about lead in Finnish clay http://www.uiah.fi/kll/research/lead.html Thanks again for all your advice. Will have a go at this next week sometime. Rod

Hi all, I'm based up in Finland and we have a lot of very clean local clay deposits. It's grey and fires to a dark red brown at the top end of it's range which I would guess is around 1100C looking at the glow. (the test we did was in a self built wood downdraft kiln without any cones or thermocouple. It started to boil and melt) There was a brick works on the site where I got the clay up until the '50's, so I know the clay is usable in some form or another. There is a LOT of clay around here, I guess as a result of glaciation? I dug a heap of clay about 15 years ago and it's been wrapped up outside getting deep frozen every year (-40C) I dried and washed a bucketful a few years ago which has been stored indoors since then. After hand wedging the clay it has a good smooth consistency but it feels quite strange. It almost like a gel?? It cracks and breaks as soon as you try to stretch it, but when you make a large ball of it, it starts to sag. If you manipulate it very slowly, say by squeezing, it deforms readily without cracking? It is not sticky at all, although in the bucket it looks like it should be as there is a fair bit of surface water on the clay. I don't have much experience with raw clay but I guess this needs an addition of a plastifier like Bentonite or Ball Clay or something? So a couple of questions... Should the clay be dried and powdered first? Or can I just work out the water content and wedge the appropriate amount of plastifier into it? ....and what percentage of plastifier would be a good place to start? Thanks in advance Rod

Thank you Sam, I'll be careful. Let's see what happens. The ground will be frozen for a couple of months yet so time to get prepared before we can start on the kiln. Take care Roderick

Thank you Marcia and thank you again Sam for another very informative reply. After looking at you web page Marcia I will just have to try soluble salts and terra sigillata in the saggar. Sam, thanks, good idea about raising the chimney wall above the lid of the saggar. re: Glazes. I've got a couple of off the shelf Raku glazes, White Crackle and Transparent to be getting on with. Then we'll see what comes up. Yes, I have an electric kiln (about 350 litre) so I can fire the saggar first. A couple of questions about this. If the saggar is castable should it still be biscuit fired first? If I make the saggar from a Raku/Crank mixture should I fire it to vitrification? Would that make it stronger? Cheers Roderick

Thank you for your thorough and comprehensive answer. It will be a simple wood fired kiln. More simple traditional ware than complicated or involved reduction practices. Multiple pots in the saggar, no combustibles included. Yes , taking the pots out as soon as glaze has matured. (so there is a possibility for post firing reduction if someone wants) Old hard bricks and hard firebricks. I built a simple downdraft kiln that went past 1100C. I will be dismantling that and using the bricks. I think this will only need to get to around 900C? I think I will fashion some kind of bellows system for extra air. I am very interested in the idea of making a "castable" ... Can you elaborate please. I am based in Finland so supplies and materials may be a bit limited. Something based on this... Possibly with charcoal packed around the saggar. (also thought that adding some rings to support some king of chimney during initial heating might speed it up?) Any other thoughts? Cheers Roderick

Hi, I am based in Finland. I want to build a simple woodfired muffle kiln for firing some Raku ware. Can anyone advise me on what clay to use for making the Muffle/Saggar ? Does anyone have experience of this? Thanks roderick