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Rich Arentzen 05-16-2015 09:32 AM

Color bubbles
Using color bars, what techniques are people using to avoid color bubbles, and what would be considered a reasonable and successful percentage of pieces without them?

Pete VanderLaan 05-16-2015 09:45 AM

In rod, when opaques using fluorine are being made, you can see bubbles completely when the rod is being made before it strikes. The rod needs to be cooled rather slowly to prevent an outgas from the rod core.

Experience tells me that lots of bubbles in rods come from putting color in your color box hot. Micro fractures occur when rod is treated that way and they show later as bubbles. There are also bubbles in rods themselves as they are being made. Bubbles get introduced into pot color from the trailing glass from gathering rod and the more rods you make, the more of those bubbles happen. I find that the upper half of a pot is suitable for good rod and anything after that needs serious inspection. I usually turned the lower 2/5ths to frit and considered my self lucky.

Now galleries and stores? They're all different. I think it depends on size and location. Some are ridiculously so stuck on perceived defects that they can't see the piece at all. I have one that doesn't want light colored transparent glass because it's hard to photograph. I would not be happy paying for a color rod that had big bubbles in it. It's not easy to make them.

Michael Ahlefeldt-Laurvig 05-17-2015 01:38 PM

I think a lot of bubbles are caused by people trying to whack off a small piece from the end of a causes fractures that make bubbles. The german color rods have gotten a lot better over the years and Id say its not a problem with the color, its operator mistakes. The trick is to hit the rod in the middle and then the middle again etc until you get the size you want- it will make a clean perpendicular break every time and no fractures.
We try to preheat the rods a bit by putting them on top of the annealer for 30 minutes or so when possible but lots of times a 4-6 inch rod will go in "cold" and they dont fracture- if they do they blowup- maybe one in 50

Eben Horton 05-17-2015 06:08 PM

Pete is right about cooling bar too fast when its made.. Riechenbach special black has a bubble to be found in about every 3 inches of it. I guess that is what makes is special. They are in there before you break it because if you are lucky, you will get lucky and crack it right on the bubble.

to avoid bubbles, i will be very careful about how i shape it before i put the starter bubble in the color... no rust on my marker or jack handles is a must, don't block it unless you know your color can take a blocking.. some colors will stick to the block. I always flash it right before i gather so the skin is warm.

Pete VanderLaan 05-17-2015 06:38 PM

This is a repetition of something I've said before but it bears repeating:

When we used to make color, particularly fluorine rods, we would gather the glass three times and then roll the rod. Speed was important to profit. Fluorine opals are transparent drawn from the pot so we could see if there were issues. We would draw a perfect rod, roll and box it. In the morning, I took one of every five rods and ran it through a diamond saw vertically to see where problems might arise. Those rods had bubbles the same size as Swiss cheese in them.

So, I changed technique and once the rod was formed, we reheated three times which slowed our process down enormously. The diamond saw work revealed a flawless rod.

Kugler for a while made rod casting them and they all had a string of bubbles down the core and to this day I believe they were having the same problem I had. Glass demands that you be patient. It doesn't tolerate shortcuts.

Dan Fenton : "Glass remembers everything you ever do to it."

Sleep on Buddy.

Greg Vriethoff 05-18-2015 04:49 AM

Here's some things I have picked-up over the years that seemingly help prevent introducing bubbles in rods. If your rods have bubbles already, there's not much you can do about it other than pick them out once the glass is nice and soft.

Some of this stuff I learned from one of Lino's assistants for anyone that cares about that.

To preheat opals (I do this mainly with Gaffer white, and pretty much any other white, enamel, etc.), take your chunk of rod and place it in a ceramic coffee mug. Fill with water to cover. Microwave on high for 1.5 to 2 minutes. Use tongs to take from cup to color oven.

For ALL colors: when taking first heat in glory hole after picking-up out of color oven - don't turn the pipe/rod. I know it goes against everything you've been taught, and it takes awhile to get used to. Apparently, the slight temperature differences in the gh environment are enough to induce thermal shock as the piece rotates in the chamber. Insert it slowly and hold it perfectly still for about 20-30 secs. It'll sag, then you can turn. I know it sounds nutty, but I've had almost no instances of popping since I adopted this technique.

Glenn Randle 05-18-2015 08:09 AM

I've found that tiny sized frit can look amazingly close to solid color.

I use #1 and #0. If you've never tried it before you will be surprised how well it covers (I always apply it in multiple layers). It is much quicker & requires less skill to apply, and there's no bubble issues to deal with. However it does consume a lot of color when you're covering large pieces.

It's not a solution to avoiding bubbles in your color bars, or creating them using poor techniques, but it is an option that can work well for certain designs. I use it for my vessel sinks.

Pete VanderLaan 05-18-2015 08:21 AM

I find that tiny frit produces a generic look every time. I'm sure it's just me. It certainly solves the bubble problem .I think it utterly fails to produce a color quality you really want to look through. It bounces back too much.

Glenn Randle 05-18-2015 10:43 AM


Originally Posted by Pete VanderLaan (Post 124001)
I find that tiny frit produces a generic look every time. I'm sure it's just me. It certainly solves the bubble problem .I think it utterly fails to produce a color quality you really want to look through. It bounces back too much.

It depends on how many layers you apply, what types of decorations are under it, and the intended placement of the final piece.

I am very pleased with the results I get on my vessel sinks. The interior color is applied in 5 layers (2 layers on the second gather, & 3 on the third), so it is quite even and dense.

I agree frit can look bad, but it works well for "certain things". I'd never realized how good it can look until I experimented with it. One thing is certain, it looks 1000% better than holes in your color. :(

Jordan Kube 05-18-2015 01:28 PM

If you're having trouble picking up large bars of opaque glasses you can turn the glory hole off just before you pick them up. Hang out in there for about 10-20 seconds and turn it back on.

David Patchen 05-18-2015 01:45 PM

All of the above, but get the basics right and you avoid lots of issues. Basics: make sure your color box or garage warms up your color reasonably (don't toss cold color into a hot box) and once hot, your rod stays on the hot side long enough. Make sure it's really hot before you stick it up! Hot = at least 1000 for most trans or 1100 for gaffer opaques. Or nevermind the numbers and just judge pickup temps as ok if its just starting to stick to the brick or slump a bit (if it's a long rod) :)

Peter Bowles 05-18-2015 08:05 PM

Certainly the right temperature is needed, and a soak (10-15-20 mins minimum) at this temperature to get the heat all the way through the bar. Getting the temp right in the hotbox negates any need to fuss with glory hole, but I would advise against going right into the flame path.

A couple of other things..

Not using too hot a post to pick up the rod in the first place - especially if you have a front loading kiln where temps at the front are cooler than the back.

Clean, sharp shears cutting through a well heated and presented bit. If you are getting any smuzz from your cut it will likely produce a series of small bubbles where it melts in.

Running the colour over a smooth heat polished post. I never use a graphite pad on gathers that will have colour run over them, I think they leave enough behind on the surface of the glass to cause problems.

Pushing the colour down with shears as part of the cutting action if you are running colour over a bubble - and definitely not lifting as you might with a foot or stem. And make sure that the colour doesn't mushroom before you tool or marver it over the post.

If there is any sort of consistency where in the piece the bubbles are showing, its probably down to technique rather than product.

Rich Arentzen 10-25-2017 07:33 AM

Back to an earlier thread
Out of 1 kg of a transparent color, treated correctly in the shop, how many bubbles would you expect to find on average?

Pete VanderLaan 10-25-2017 08:14 AM

"treated correctly in the shop" is pretty vague especially considering differing levels of experience on the board.

You sound like you're fishing.

People who make color are judged an inch at a time. Levels of trapped gas go up as you go down in the pot for a variety of reasons mostly from gathering. In our act, we did not use the glass on the very top, particularly in leaded rod and then could successfully make rod until the pot was about 1/3rd full. We took fully blown out first gather proofs of color as we made rod every fifth rod. If it began to decline in quality we converted to frit. The rest was ladled and crushed to make frit.
Most color rods are fairly opaque when trying to see thru them and I don't think that ultrasound is really effective.

If I wanted absolutely bubble free color, I would learn to make my own. Perfect rod isn't going to happen and I really don't understand why people think it would happen.

Rich Arentzen 10-25-2017 09:58 AM

Thanks Pete,

Indeed, I am not looking for perfection, and yes I am fishing for a benchmark by which I can see what level of imperfection I can safely predict.

Pete VanderLaan 10-25-2017 10:24 AM

well, you can see from prior post that they can be introduced in the factory or they can be introduced in your shop. Bubbles are inevitable in the factory. What should not be tolerated are stones. I don't think there's any fixed benchmark. Some colors are harder than others. Getting in a hurry causes problems in both places.
Try simply doing it with a tank of clear and you'll get a notion of how hard it is even when you can see the bubbles. Put the clear rod in the color box and see what sorts of things occur. Clear witness pieces are useful at every level of production.

Eben Horton 10-25-2017 11:39 AM

Are you having this problem with just 1 color? If so, raise the pick up temp 10 degre increments until your color slumps, then back it down 10 degrees.

Are you using Gaffer and richenbach? Gaffer likes a higher pick up temp. Plaques from Gaffer especially so.

Greg Vriethoff 10-25-2017 12:26 PM

Those Gaffer plaques are beautiful for sure.

Jordan Kube 10-25-2017 12:41 PM

A couple of bubbles per bar, Rich.

We pick up half bars of gaffer opaques and have to bring them up to 1060 so they don't crack. Micro cracks from not having them hot enough are also a source of bubbles.

Eben Horton 10-25-2017 01:06 PM


Originally Posted by Greg Vriethoff (Post 137094)
Those Gaffer plaques are beautiful for sure.

Especially the yellows.

Ted Trower 11-01-2017 01:39 PM

I suspect that rapid cooling creates bubbles in color bars the same way they form in a Prince Rupert drop. The exterior solidifies before the core goes thru it's thermal shrinkage and somethings gotta give.

Also I work out of a public facility so the color box is always hot when I get there. I have found I get fewer cracks in my color If I set a cold piece of kiln shelf under it when boxing for warm up.

Marc Carmen 11-01-2017 03:25 PM

Color bar straight into a 1025f box is usually not a problem so long as the piece is small and it goes in on a cold shelf.

Larger pieces of color, lead free color, dark colors, and any combo of these will get micro cracks. What usually solves this is placing a small square of kiln shelf atop the chunk, or even a stainless cocktail shaker over the rod in addition to placing it on a cold shelf. Then just remove the cover 10 mins into heating. Dark lead free colors are usually the worst with cracking (homemade transparents, nero duro) as they absorb the light from the elements as well as maybe being more brittle than the lead stuff.

Josh Bernbaum 11-02-2017 08:55 AM

Is anyone using Gaffer's new "Durissimo" black? It's crazy stuff. I've found that with my setup, if I don't preheat to 1250F it cracks after going to hole. It has to be the only thing in my pickup oven at the time of course.. For comparison, the other Gaffer opaques I take to between 1075 and 1130 depending on color.

Pete VanderLaan 11-02-2017 10:38 AM

It is simply a suspicion but stiff glasses tend to have high alumina contents which are going to be dicey expanding in a color box.

If you remember the trick of taking any glass from a pot and then hitting it with a cold concentrated blast of air from the compressor, when you stop, big bubbles appear in the gather, then as the gather stabilizes, those bubbles begin to shrink and go back into solution. If you do mole chemistry calcs on a glass, you can see all the dissolved gases in the glass.
I think it's reasonable to get suspicious of those gases being in the color but in solution. I think it's reasonable to get suspicious that heating and cooling the rod may trigger a path for the release of gas into a visible section of the color.

I've done this for a long time. In that time, I've seen a lot of chemical phenomenon in glass to the point than none surprise me. It's glass. Expecting no issues from glass is probably going to leave you unhappy if you have to promise perfection.

Marc Carmen 11-02-2017 11:34 AM

Josh, I'm dying to try the durissimo. If it's a similar formula to Nero duro then it's a lead free iron sulfide black. Iron sulfide glass is not only naturally stiff but also incredibly brittle. Old glass container literature mentions that it is a cheap and easy way to black glass, if only it didn't make such an impractically brittle bottle.

Man, I have sooo many bubbly black filigrana in my student work haha.

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