New bubbles that weren't occuring before

[theanimallover]

I've been using the exact same program and the same materials for a couple of years, and I've noticed that I'm getting more bubbles in my work recently. Could this be somehow due to having an oldish kiln? I can't think what has changed that would do this. I work with black glass, then copper then capped with clear.

The only thing that has changed is my cleaning method. I no longer use water and bubbles and then spray with glass cleaner, I just use glass cleaner which has helped with devit.

Thanks,
K

[David Jenkins]

What are "bubbles" in the context of your cleaning regimen?

[theanimallover]

Hi,
I used to use Ecover - environmentally friendly washing up liquid, then I'd dry and spray and clean with Bohle glass cleaner. The problem was that a lot of pieces had a haze over them, so I started to ditch the washing-up-liquid and just use the glass cleaner, this has worked well so far as the end result is nice and shiny. But now I am having bubble problems, there are noticeably more bubbles and a lot of my pieces are wasted. But saying that, this didn't happen over night when I ditched the liquid it has happened over the last couple of weeks.

I am wondering if the paper towels I am using to clean my work with the glass cleaner have left 'bits' on the glass as I noticed they seemed quite dusty to use.

Also, although I have used the same schedule for 2 years, I'm wondering whether to change it to help eliminate bubbles, as during this time I've had a lot of pieces wasted though bubbles. Most of my work involves two pieces of glass with copper sandwiched between.

My schedule is 330 to 750 hold 10, 500 to 1150 hold 30 then 200 to 1250 and hold for 2hours. Would it help do you think if I slowed to 250 to 1100 then slowed right down to 50 to 1250?

Thanks

[Stephen Richard]

I'm really unclear on what you are doing and the results you are getting. A picture would help.
Whether you are using S96 or bullseye, I find it odd that you are doing all your work at 677C. That is in the area of a Bullseye bubble squeeze.
For the bubble squeeze you might try moving from 600C to 677C at 50C/hr.

Has your copper source changed? Is it as easy as before to get it flat?

Possible change of practice: Tack fuse the copper to the back of your glass - put copper on kiln washed shelf, glass on top, fire. Then clean and put bottom layer on and fuse.

I normally try to get my work done with a 10 min. soak. Your long soak is at the bottom end of the devit range.

ps. temperature conversions are at the top of the page.

[theanimallover]

Hi thanks for getting back to me, I am using bullseye glass.

You should be able to see the hare - this is an old piece that I kept as the design was wrong, but as you can see where the silhouette is (black) there are hardly any bubbles, but if you look at the dog - which has just come out of the kiln, there are lots of big bubbles - I didn't get this before, or rarely, especially with the dog.

For a couple of years I fired my pieces with no problems except the odd failure, now I am getting lots of failures. I can't understand what I am doing wrong. Perhaps my kiln is getting old?

I am using the same copper as before from the same place.

Karen

[Jenna]

Hi Karen,
Do you fire your pieces dirrectly on a kiln shelf?
Are you perhaps using a new or different kiln shelf? Or, if you are using an older or the same kiln shelf (you said that you haven't changed anything else), has it perhaps degraded some after many firings? What I'm thinking is that perhaps there are some small indentations or nicks in your shelf that could be trapping air between your glass and the shelf and giving you those bubbles.
Just a thought.
Jenna

[Warren Weiss]

Karen,
The bubbles are not from the kiln shelf or cleaning. They are from air trapped between the copper design layer and the clear glass cap. In the picture there appears to be texture in the copper sheet which is an invitation to bubbles. As someone mentioned that fireing face down without the clear cap will allow a smooth surface for then applying the clear cap in a second fireing, if that doesn't change the copper color appearance. Either way, a revised bubble squeeze fireing schedule as mentioned by Stephen Richard should improve the situation. In addition, if doing in one fireing as you are doing now, you may want to put a tiny chip of the cap glass in each of the four corners. That would aid by allowing the center of the cap glass to sag down first during the fireing leaving an escape for the air between the layers.

[theanimallover]

Thanks Warren & Jenna,

I'm pretty sure it's not the shelf as the air is trapped between the glass not under the glass.

I have been making coasters like this for 2-3 years and experimented widely. I did try chips of glass and firing upside down, but neither helped.
What I did in the end is revised my designs to minimalise bubbles. So the dog design you see was coming out fine each firing for at least a year or two, so I can't work out why it's not working now. I fired 6 and only 2 were good

I will revise my schedule and suggested.
I'll slow the rate to 1250F, should I still hold for 2 hours here?
Thanks.

[Stephen Richard]

Are you looking to have the edges of the piece rounded? If so, then there is no reason to avoid going to 804C for a full fuse. You only need 10 mins there to get the rounded edges.

As you say it is clear that something has changed. Review each element of your practice in turn. Also review the materials.
I can't see the texture of the copper, but having a 100 mm square of thick steel and a jewellers hammer will enable you to get the copper really flat and so help minimise the bubbles.

[theanimallover]

The copper is pretty thin, almost rippable. It is usually pretty flat, I think the picture distorts it as it's not that wrinkly!
Thanks for your help.

[theanimallover]

Actually, I just remembered I am using a new tube of glastac - it does seem very runny - but it's the same make that i always use.
Also, the copper I have arrived a bit damaged - looked like the end of a roll as it had a line through it, perhaps something was deposited on it.
Anyway, next firing I'll slow down and clean the copper, and make sure it is 'flat flat'.

[Stephen Richard]

Where do you use the glasstac? how much? why?

[Morganica]

Even if the copper is flat here's still enough space for a little air between the glass and the copper, and the glass and the glass. The thing about trapped air is that it likes to travel to the point of least resistance and usually combines to make bigger bubbles. So it would be tough to have a completely bubble-free piece of foil that big, trapped between two pieces of glass, without at least some bubbles...even flatter than flat. I missed the type of glass you're using but if it's hand-rolled, there's already some space there that could trap bubbles.

If the copper you're using is creased or crumpled and smoothed out, it may be trapping a little more air than usual. And if there's something contaminating the copper, there's even more potential to generate bubbles. Cleaning the copper well and making it flat will help. Chadding the edges, increasing your bubble squeeze and reducing the top temp will help. If your glass is hand-rolled, prefiring it to flatten out the surface will also help.

[theanimallover]

I've found that it is impossible to get rid of all the bubbles, so I am happy to live with them - but it's only recently they have become so large on so many pieces.

Anyway, this firing I really smoothed down the copper, and slowed down the rate right down to 1250, and the results were a lot better - out of 6 coasters, one was a bit spoilt through bubbles - so quite a good result. Morganica, I am using Bullseye black opal and tektra clear. How would you clean the copper? I did have a stage where I scrubbed the copper with a green scouer, I'm not sure if it stopped the bubbles, it did make the copper look different though.

Stephen, I use glasstac to hold the copper down as it's hard to get the clear cap on without moving the copper slightly, I use sparingly. I don't wait for it to dry, just the stickyness holds the copper in place.This firing, I did use less, but I still used it. I was told (on this board?) some year's ago that using glasstac shouldn't make any difference to bubbles. Could this be adding to my bubble problems? It's strange, but this new bottle does seem really runny.

Thanks
K

[Morganica]

The Glasstac (or anything else you apply) has a certain amount of water and it has to go somewhere when it vaporizes. Generally you don't use enough of it to make a difference in bubbles, so it's not an issue. Use a lot, and it might be. Either way, an adhesive layer will very slightly raise the foil off the glass in spots (the thickness of the glasstac under the foil). The adjacent areas would hold a bit more air than if the copper were simply flat on the glass...so you might see more or bigger bubbles.

You might try shortening the schedule a little bit because the size of the bubbles is at least in part a function of the time they have to join up and get bigger. I believe the black opal is hand-rolled, which means it's going to have uneven spots that trap air. Try prefiring the black--cut the piece maybe an inch or so bigger than you really need, and give it a fast full fuse (IOW, don't let it stay at process temps long enough to start pulling in and making holes). That will give you flat-but-slightly-domed surface profile, exactly what you need to drive out air. Then just cut the sheet to size and proceed.

I've been told this works but I've never tried it so you'll want to experiment first: Put down your bottom glass (the black), put the foil on it, and cover with a thin layer of clear or crystal clear powder, just enough to turn things white. Fire that in a full fuse, then cap and fire again. Like I said, I've never tried this, and I would wonder if the foil wouldn't curl, or maybe the powder would melt together and make holes...but I'm assured that this is the way enamelists do it. Dunno, might be worth a try.

On cleaning copper: At the very least I polish off the oxidation on the copper. If I think the metal I'm using has some kind of contamination, deposit or coating, and I'm not sure what it is, I'll wipe it down with denatured alcohol and acetone, wash it in detergent with a scrubbie or steel wool, rinse it in a vinegar solution and then flood with clean water. It's probably overkill, but I'm trying to hit it with a variety of solvents to make sure I've really removed all the crud. So far it's what works best for me; I know other people who simply scrub with warm soapy water and do just fine.

[Stephen Richard]

YOu could try hairspray instead of glastac as your positioning adhesive. Much less volume and does have a tackiness to hold pieces in place while the cap goes on.

[theanimallover]

Hi Morganica,
When you say shorten the schedule, at which point?
Thanks for the info on sprinkling the copper then capping. I think though the copper would go blue...I'll try and experiment some time!
I'll give the next batch a scrub, see if that helps. Also, I have new copper coming soon, so I'll see if it was just a 'dirty' batch.

Stephen, I think I'll first try and stop using glasstac, see if things improve. Hairspray is a good idea as glasstac always comes in in big globules.

Thanks.

[S.TImmerman]

I have cleaned a Lot a of copper and I always use baking soda. I make a paste with vinegar and use this on a scrubby pad. I don't know if this will help but I wanted to try;)
St

[Morganica]

Hi Morganica,
When you say shorten the schedule, at which point?
Thanks for the info on sprinkling the copper then capping. I think though the copper would go blue...I'll try and experiment some time!
I'll give the next batch a scrub, see if that helps. Also, I have new copper coming soon, so I'll see if it was just a 'dirty' batch.

Stephen, I think I'll first try and stop using glasstac, see if things improve. Hairspray is a good idea as glasstac always comes in in big globules.

Thanks.

Sorry, I meant at the top process temps, when the glass is flowing.

[theanimallover]

It amazes me the amount of scientific knowledge glass people have!
I've just made a batch that have come out bubbless! I have a new problem now though - but minor compared to the bubbles - the copper is now burning too hot and turning blue...

I'm guessing that where I've slowed down the speed from 200 to 50 going to 1250 this is causing the copper to get too hot. It must be this as it hasn't done this before.

I'm going to experiment with speeding up a wee bit.

Thanks. K