Devitrified knobs

[JaySpangles]

I have made a set of cupboard door knobs for my bathroom on my Minor.  All lovely and shiny. 
Unfortunately I ran out of glass (Vetro sweet lime).

Now I have some more, I have made some more knobs for the same set but I had to use a Hothead this time, and all this new batch has devitrified (or at least I am assuming that's the cause of the matt finish on the Hothead ones)

I still need to make more, and have only the Hothead to work on.  They did take longer to make so were in the flame quite a long time.  Is there anything I can do to prevent it happening again.  The matt ones look OK but I prefer the shiny finish on the first batch.

Thanks for any help.  I did search the back posts but most seemed to refer to slumping and fusing.

[JaySpangles]

Oh well, as no one has come up with any solutions to my little problem I have painted one of them with clear nail varnish.  It has restored the glossy shine, and as it is on a drawer that doesn't get opened too often I will wait with baited breath to see how long it lasts before I do the others.

[Cecilia]

Have you tried coke or cillit bang I seem to think they have been sugestions in the past. I have tried the coke but I am not sure it made a huge difference...
X

[JaySpangles]

I haven't, but I will.  There are a few varieties though, maybe the one for lime scale removal might be appropriate.  Come to think of it I have some Viakal in my cupboard which is brilliant at lime scale removal, I might try that as well!

[Glyn Burton]

I suppose you could try acid polishing but it is a fearsomely evil mix to use.

[GaysieMay]

I think I've got a similar problem with some of mine Janet - think I've had mine in the flame too long - I'm using a real Heath Robinson affair to try and make them!  I've seen some threaded rod in BQ though so think I will buy some and chop them up into usable lengths.    Think I'm going to acid etch mine!

[Pat from Canvey]

Hotline Spray "A" overglaze is used on sheet glass that devitrifies when fused so that might be an option. Perhaps cover the knob with the glaze and put into a cold kiln and bring up to annealing temperature but try first with an experimental piece of the same glass. Another similar type thought is to use the frit used to make sugar beads. Put knob in cold kiln and bring up to anneal temperature. Take out of kiln and introduce to flame slowly. Then cover with the frit, melt. and put back in kiln.
see http://www.pearsonsglass.com/p449/Spray-A-Overglaze-472ml/product_info.html

[MeadMoon]

Hi Pat,

Do you use the "Spray A" after the glass has devitrified or use it as a preventative before firing?  I've made a couple of bowls from recycled bottle glass and one of them has devitrified quite badly, maybe because I wasn't vigorous enough when removing the gunge under where the label was.  Borax solution has also been mentioned as a means of preventing devitrification.

[Pat from Canvey]

Elaine, in all honesty, I just can't remember whether it was before or after devitrification as it's literally years since I used some. I rather think I used it as a preventative, but perhaps those who fuse for a living can chip in.

[JaySpangles]

Thanks for the link Pat, I will try that when I get back to the UK.

[jeannette]

Well I have seen this recommended, but not researched a UK equivalent
http://www.amazon.com/gp/product/B000MQN3VU/ref=as_li_ss_tl?ie=UTF8&tag=fuseglassorg-20&linkCode=as2&camp=217145&creative=399373&creativeASIN=B000MQN3VU

[JaySpangles]

I can only assume that an etching solution will result in a mat finish, when really what I want is the glossy glassy finish to match the ones that didn't devitrify when I made them with my minor. Thanks for the suggestion.  Perhaps I have misunderstood.

[jeannette]

Yes, you are right - I have seen the use of this that creates a matt finish and then followed by a kiln polish. Sorry about that...

Edit: My tutor called it kiln polish, but just found a reference here for fire polish http://www.frit-happens.co.uk/forum/index.php?topic=112.0.
I'm sure I read something about flame fire polishing, but can't find it, sorry. It's a fast schedule, but I haven't tried it myself on this schedul. I think Rachel, aka Flyingcheesetoastie also posted a schedule but I can't find that either,

As you imply - it's best to avoid it I should think - not sure how.

[JaySpangles]

How does the kiln polish work?  Do you just put them in a cold kiln and slowly bring them up to heat?