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birdypotter

Help! Nichrome Wire Leaving Green Stains On White Stoneware

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I use nichrome wire hooks to hang decorations no larger than half the size of the palm of your hand and no thicker than 5mm, though often a lot smaller and a lot thinner. I've been using hooks as the decorations are fairly heavy and so I use thick bead rods - too thick to thread directly through the holes made in the clay. (If anybody could suggest a better method I'm open to making my life easier, bending 100 pieces of wire and hanging takes a lifetime!) The wire itself is sturdy and doesn't slump, however I use a white stoneware body, decorated and transparently glazed. After a stoneware glaze firing (I glaze to 1250) I have what I can only describe as green burn marks above the area where I've cut the hole, right where the wire sits, though the wire does not touch the piece.

 

I thought it might be the wire getting old, it can become quite black and brittle after several firings. However after replacing it with new wire I have the same problem on the first firing. I can't remember it being a problem I've always had, and I've tried several different clays recently in a sampling run - it's happened with all of them, so just trying to rule things out. It's ruining what would otherwise be completely saleable work and I'm totally confused! I really hope I'm missing something obvious here; can anybody shed some light please!?

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I can't shed any light on the reason, but I will say that I have also had that same problem with stilts... So I'm interested to hear what anyone else has to say about the issue.

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http://www.pelicanwire.com/products/resistance-wire/

According to this site, nichrome wire melts at 1400 C. I would suggest that maybe it's beginning to off-gas at your glaze temperature, which could explain the green mark. Chrome flashes out of some glazes like this, making chrome/tin pink.

 

I'm not totally knowledgable about bead wires, so if anyone else wants to chime in on this...

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Sure sounds like volatile impurities coming off the wire.  Is it worse with new wire than old? Lubricants are used when drawing wire Molybdenum disulphide is commonly used and may adhere to the surface of new wire if the wire was not cleaned thoroughly in manufacture. I don't know what color Molybdenum would impart to a glaze. If this is a surface contamination problem, then it should go away with further firings. Old wires should be better than new ones. If it is contamination in the wire itself ( probably most wire you get now is made in China and their quality control sucks)  then there is not much you can do except try a different batch of wire.

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It was as bad with the old wire as it was with the new. On top of the green marks its probably worth mentioning that it leaves a lot of black dust deposits after a firing which can't be healthy for my kiln!I wonder if trying a different wire altogether would work? Perhaps kanthal?

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Have you tried Kanthal wire? I believe it is rated for higher temperatures than Nichrome. I have used it for years for attaching buttons fiber to the structure in raku kilns. This link provides insight into the characteristics of the two res.

 

http://temcocontent.com/resistance_wire_faq.html

 

Marcia

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Update:

 

Hi, thank you to all that gave suggestions. For anybody looking at this post down the line who is having the same problem, I dropped the temp to 1180 with a new batch of nichrome but the green flashes were still a problem and so have tried the same tests, as Marcia suggested, with a batch of kanthal wire - success!

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Hi Pugaboo, I'm UK based so I got my wire from the supplier Potclays in Stoke-On-Trent

 

....however this should help if you were wondering which one was best to get, helps me to know what to type in next time I go hunting for some!

http://kanthal.com/en/products/materials-in-wire-and-strip-form/wire/resistance-heating-wire-and-resistance-wire/

 

http://kanthal.com/en/products/materials-in-wire-and-strip-form/wire/resistance-heating-wire-and-resistance-wire/list-of-fecral-alloys/

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Hi Birdypotter

 

Thank you for the links - I'm wondering what gauge wire you used?  I'm wanting to make a "space separator" hanging with many tiles - approx 3/4in wide with 3-6in lengths.  My goal is to glaze both sides however I've never done such a thing.  I'm finding it difficult to get Nichrome wire and after reading your post (I'd like to fire cone 6 and cone 10 stoneware) I'm wondering if Kanthal is my answer.  Our pottery supply shops don't seem to carry much so I will probably have to order from the UK

 

Thank you

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Hi Birdypotter

 

Thank you for the links - I'm wondering what gauge wire you used?  I'm wanting to make a "space separator" hanging with many tiles - approx 3/4in wide with 3-6in lengths.  My goal is to glaze both sides however I've never done such a thing.  I'm finding it difficult to get Nichrome wire and after reading your post (I'd like to fire cone 6 and cone 10 stoneware) I'm wondering if Kanthal is my answer.  Our pottery supply shops don't seem to carry much so I will probably have to order from the UK

 

Thank you

 not sure if I'm reading your question right. wire for racks or stilts? racks like these?  I think they sag above about ^5-6 though.

 

star-bead-rack-7p-of-10-wire.jpg

 

lots of suppliers online, this one from here: http://www.bigceramicstore.com/kilns/kiln-furniture/bead-racks.html  just try searching "bead racks kiln". You can buy just the wire and make your own supports.

 

for wire for stilts euclids sells different gauges http://www.euclids.com/index.php?cat_id=159

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Mead,

 

I make hooks and loops to hang decorations, and often fire up to cone 6-7. I use 0.9 for my lighter pieces and 1.4 for my heavier pieces to avoid sagging. Unfortunately kanthal is far more brittle than nichrome at higher temps so I have to refresh my stock fairly regularly. I've started buying from a local supplier who repairs kilns - if you have somebody similar nearby they may be able to help supply you. 

 

Also: The same man who sold me the kanthal wire told me recently that painting bat wash on to nichrome wire before firing it helps eliminate the green flashes - I've since gone over to kanthal so haven't tried this but it might be a temporary fix for anybody experiencing the green flash problem? 

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