raku glaze

[ps_bond]

Ah, it's for firing? The zinc will fume off, and in sufficient quantities can give rise to metal fume fever (yes, it's a killer) - so there's your poisonous gases. Horrible stuff. Oh, the zinc oxide also deposits onto everything going, contaminating welds, glazes, everything.

However... If galv is all you have, you can (relatively) safely pickle the zinc off using acid - I've used brick cleaner from B&Q, 10% sulphuric or vinegar on occasion, the vinegar being the slowest; it will fizz and generate hydrogen as the zinc reacts with the acid. Once the reaction stops, I add a small amount more acid and see if there is any zinc left to react.

In the case of sulphuric acid, the resulting solution is a mix of the acid and zinc sulphate, not much worse than used pickle really; the steel will need to be washed and preferably neutralised in e.g. bicarb, but it'll be clean of zinc.

Zinc fuming shows as a white smoke at heat - you'll see it if you melt brass, get it too hot and more fumes off. Solder contains some, but in such small quantities that proper ventilation is aduquate. You can burn it off in a forge, but it is a really, really unwise thing to do - here's an object lesson: http://www.anvilfire.com/iForge/tutor/safety3/index.htm

Usually caveats - handling acids, alkalis, generating flammable gases, ventilate, working at heat etc. etc.

[jille]

thanks peter for all the info, i certainly won't be firing glavanised steel!!

[PureGold]

Wonder if these might help you as they seem to do metal bead racks for raku kilns...http://www.ceramatech.co.uk/6.html

[jille]

thanks for the link, I have saved the website, those bead racks look good but I can't find the prices.
I just want to mention as i see they sell Nabertherm kilns, I have had no end of trouble with mine from the day i got it.

[fay144]

Hi, just wanted to update this with my results so far.

I had a go at using raku glaze, totally unsuccessfully. I tried it on copper, and the glaze just chipped off after firing. I didn't really want to waste any silver, and figured it would be the same as copper. It must be something about the nature of silver clay that lets the glaze adhere better. I'll give it another go when I get round to getting some silver clay.

On the up side, I tried raku firing enamel while I was setting fire to things anyway... that was more interesting, if a bit frustrating. I had one really good result with a green enamel, but struggled to repeat it. I had a few ok results, and the rest were largely unaffected by the raku process. It was an interesting afternoon regardless though, even if it didn't produce any master pieces.

[Kwant]

Hello Fay, sorry to hear things did not go as expected, perhaps it is the slightly porous nature of PMC that gave better results. Having said that, I am slightly at a loss as to why you would even want to raku fire silver, as in my experience of using ordinary raku clay with raku glazes and oxides they often give beautiful metallics in any case and I cannot quite see the point of trying it on silver in the first place. Do you have some pics of what happened with the precious metal clay?

[jille]

I'd love to see pictures too.
The silverclay piece in the book looks lovely, it made me want to have a go but I am playing with clay for the next few weeks.
I did some raku on enamelled copper and after a few pieces i managed to work out how to get a good effect but as i didn't keep notes I'll have to go back and start again, My enamelling kiln doesn't have a pyrometer so it's hard to know the temperature so it's a bit hit and miss for me anyway, i quite like that though.

[fay144]

Kwant - sorry, I've tried to find the photo from the book that I could post, but can't find a copy online. It was a very interesting effect - in the project in the book he created a donut shaped hollow silver form, and then dipped it in the glaze, so less than half of the surface was glazed. It was a very different effect to enamelling. It seemed worth a go.... I think you are right though, it must be the porous nature of PMC.

Jillie - yes, I'm definitely going to give the raku enamelling another go at some point, and I agree that unpredictibility can make things interesting sometimes! Did you use sawdust, and how long did you leave the piece in the sawdust for, if you remember? I wasn't really sure if I was leaving it long enough...

[Kwant]

Np Fay thanks for looking, as far as how long to leave things in the sawdust, leaves what have you, it is the fire and smoke caused by the hot piece being put into the combustible material that causes the effects so as soon as the fire is out and the smoke is gone is long enough.

[jille]

I used newspaper and a tin lid for the copper pieces. When I did raku bowls we used sawdust. i think it's good to try different things, we got flecks on the pots where the sawdust landed on them, not sure that would be a good look for copper tho.
I have ordered clay and raku glazes from Bath potters, i can't wait to use my new bead rack out. I might play with porcelain while I'm waiting