annealing after sandblasting?

[Megan_in_BK]

Is it okay to anneal boro after sandblasting it?

[steven p selchow]

yes..Ive made many pieces that I wanted to remove the blast in certian areas, and kilning it was the only way...never a crack so far..go for it.

steve

[SNYD]

all work should be annealed after coldworking, whether sandblasting, cutting and polishing, etc. You are putting stress back in the glass when coldworking.

[Icarus]

Really? That's good to know. In the sandblasting class that I took, the instructor said that putting the piece back in the kiln would have the same effect as flame polishing the piece, and would effectively remove the "whiteness" produced by the etching.

[steven p selchow]

I don't know why he gave you that info. annealing a sandblasted piece changes nothing, the only way to remove where you blasted is to fire polish in a reduced flame, It tends to bubble up where you fire polish it, but you can get it back to clear, or the color it was by doing it slowly..hope that helps. I just did a scuba diver and sandblasted it, rather than tape off where I didn't want it blasted, it was a small area on the goggles, it went back to a polished cobalt, kinda neat looking.

steve

[stackerson]

im with snyd. although i have no practical sand blasting experience i have many friends that do and i would have to agree that any coldworking will induce stress and stress points. and should therefore be annealed after the process to eliminate said stress. just my .02 tho

[NUBBLET]

I thought it common sense , the surface tension of the glass has been broken , surface tension has a lot in play, in the annealing process right ?

[puddletown]

surface tension has a lot to do with the structural integrity of the piece if it has been tempered, but im not so sure about annealed.

[Icarus]

I don't know why he gave you that info. annealing a sandblasted piece changes nothing, the only way to remove where you blasted is to fire polish in a reduced flame...


I thought it common sense , the surface tension of the glass has been broken , surface tension has a lot in play, in the annealing process right ?

Man, that is so good to hear. I thought all of that info seemed wrong. When she siad that, I was like "jesus, how hot is it in your kiln?" It seemed like kind of a risk, making a piece, and then intentionally creating millions of tiny little stress points on the piece.... and then doing nothing.

Thanks for the input on all that, and Meghan, thanks for putting up this thread. I love it when you learn something really important by accident.

[lucidvisions]

I was under the impression that you did not have to anneal after sandblasting. Wasn't it already annealed? I'm pretty sure that the only reason to anneal a sandblasted piece is if you've reintroduced heat to it. Even if you anneal it after blasting, the surface stress of blasting will always be present no matter how many times you anneal it again.

Josh

[Greymatter Glass]

I see Josh's point. You can't anneal out a scratch or surface "flaw" so annealing a sandblasted piece seems redundant. On the surface I agree. No pun intended.

But there's also the issue of vibration. As you sand blast, cold work, polish, etch, etc you're inducing micro vibrations that can in theory impart further stress on a piece. It's like dropping a piece on the floor over and over - it weakens the glass and eventually dropping it over and over will break it. Annealing can remove the "memory" of being vibrated.

Ultimately I think it's a matter of "best practice" even if you don't fully understand the mechanics of it the fact that so many people do anneal their work after cold working is a good sign you should too. I know Andrew Brown anneals all his cold worked pieces after cutting/polishing them, and I've seen the result of NOT annealing them soon enough. Stuff has fallen apart on his table between cutting and annealing - I can't say if it's a problem annealing would have helped or not, but I know I haven't seen a finished and re annealed piece do the same (maybe he has, I haven't). It's not a physical proof in the scientific term, but it's practical proof that annealing seems to play a role in the stability of his work long term. Because of that I tend to re anneal most of my work when I cold work it.

[steven p selchow]

Josh is right on. I guess maybe I didn't explain enough. Im talking about a boro piece thats not cold worked, just made and blasted. If your smart, yes the piece shold have been already annealed before blasting, Im refering to just wanting to remove a area of the blast..in that case, it has to be re-annealed to prevent cracking, as far as cold working a blasted piece, then polishing it that way I've never done it, but I'm a figurative worker.

[NUBBLET]

anneal it after sandblasting .

[lucidvisions]

If you have made a piece and not annealed it before sandblasting then anneal it. If you don't anneal a piece before sandblasting That's just crazy. I'm so confused on how annealing your piece yet again after sandblasting will do anything. If anything sandblasting will show you if your piece was annealed right in the first place. If you annealed it right the first time you have released all the stresses on on the glass due to heat. The stress you put on glass while sandblasting has nothing to do with heat thus not needing another annealing cycle. Do you really think that annealing it again will remove the memory of it being sandblasted?

I hope I'm not coming off as arrogant in this thread it just baffles me that you could release the stress of sandblasting with an annealing cycle. The only way I would know how to do that would be to flame polish it all off......and yes, then you'd have to reanneal it.

Josh

[NUBBLET]

if stress is added (any kind of stress) you should anneal the piece . Annealing removes ANY stress by bringing the glass to a temp that allows the molecules to align and eliminate most stress , the second part comes in the cooling and allows the molecules to continue shifting until it is at a state of non fluidity so it has very little stress in its cooled state .

The temp used will not or should not change the shape of the piece so blasting will still be there but the stress CAUSED by blasting will be eliminated .


ANNEALING IS NOT FOR ANY COSMETIC PURPOSE IT IS FOR ELIMINATING THE STRESS IN THE GLASS , so you will not anneal the marks out but will anneal the stress that can cause failure out .

whatever tho I will try and shut my ass up .

[lucidvisions]

No, whatever Nubblet, don't shut up. I think discussion on any subject is justified. Debate is paramount in getting the true answers. Mickelsen needs to chime in here and he'd probably put an end to any debate. I will not pretend to know all and can always be educated more fully.

My understanding is that annealing glass will only remove the heat induced stress. If we score a piece of rod and then anneal it will the stress of the score be removed?

Josh

[byron3]

Yes, annealing removes stress no matter what the cause is. Will the score still be there? Yes, but anneal it and then try to snap it............

[Swampy]

Well, I don't know, but I just do what I do and no complaints so far.

I don't anneal anything after sandblasting it. However, all I'm doing is lightly abrading the surface to leave a permanent mark, not deep carving.

When I had the studio in UK I had bigger equipment and I did one or two full size door panels per week. Although the glass was laminated, as in; two thin sheets with a silicon layer between them.

[steven p selchow]

Been awhile since I've been here. First off, Megan never mentioned if it was a cold worked piece she blasted then wanted polished, or just a solid piece she made and wanted to remove some blast she did on it. But Im glad cold worked got somehow put in this thread, even though she may not of been refering to this. Adds information which is good. Say I made a piece, annealed it, then wanted to blast it, but, I decided to remove some of the sandblasted piece in a certian area, I know taping off is the best way to not blast where you don't want it, but In my case it was such a small area, I knew I could remove the blasted area in the flame, but in order to do it, it would have cracked, thats why I had to re-anneal it before I removed that area to fire polish, thats all I'm saying, we should all know you can't just plunge a cold piece thats already been made and annealed, sandblasted or not into a torch and not expect it to crack like hell, with the exception of say you made a tree, and the very end of it had a small check in it..you don't need to anneal the whole tree to remove the crack just on the tip of a branch, a small cool flame and you can get away with it, but you also can just open the kiln, and put that little area you fixed into the kiln with the rest hanging out, just saying, if thats what makes you feel more comfortable of the crack not coming back, I don't beleive it would anyway, just from my own experience. Mickelsen could be usefull on this but he glues a lot of sections together that have been annealed already..thanks for the participation in the thread all.

steve

[Robert Mickelsen]

Interesting discussion. I have to comment. I know from experience that if you do not anneal before sandblasting, the etching of the surface will encourage the release of the stresses in the glass, causing cracking. If you anneal before blasting, the glass will not crack. It will not crack because there is no more stress in the glass. Sandblasting does not introduce stress into the glass. Here is why.

Glass exists in two states: elastic and plastic. As you ramp up through the temperature scale the glass changes from one to the other. At room temperature the glass is entirely elastic, meaning it can be distorted using pressure, but will always return to its original shape unchanged. If you introduce too much pressure, however, it can break. This is what happens when you drop glass and it breaks. As glass heats up, it eventually reaches a point where it begins to lose elasticity. Below this temperature, glass will not "remember" stress. At this temperature, it will begin to "remember". This point is called the strain point. Another hundred or so degrees higher is the annealing point and another several hundred degrees above that is the softening point. At the softening point the glass becomes entirely plastic. Any distortion applied to the glass will remain.

Any stress that is introduced to the glass below the strain point will not be "remembered" and this includes cold working. It is possible to stress the glass in a number of ways when it is cold. Apply too much stress and it will break. But release the stress before breaking and the glass will return to its original shape unchanged.

Coldworking can introduce weakness (not the same as stress) to the structure of the glass. When you score a piece of rod to break it, you break the "skin" and make the glass weak. Annealing will not "fix" this. You can test this by scoring a piece of rod as you would to break it, then anneal it and see if it still breaks at the score.

- RAM

[boxfan willy]

Great thread. Thanks for saving me an annealing cycle.

[jr23]

I second that I just droped a blasted piece that had not been re-annealed and it really blew up when it hit the table.

I totally was ignorant of the discussed info and I too thought it was a annealing problem.

cause the piece was chunky with good welds and it went into like 30 pieces.

You guys think that blasted glass is strong as blasted of the same size shape.

[Robert Mickelsen]

But there's also the issue of vibration. As you sand blast, cold work, polish, etch, etc you're inducing micro vibrations that can in theory impart further stress on a piece. It's like dropping a piece on the floor over and over - it weakens the glass and eventually dropping it over and over will break it. Annealing can remove the "memory" of being vibrated.
This is not accurate. Glass has no "memory" in its elastic state. Drop glass repeatedly on the floor and you damage the surface. Compromising the surface makes the glass weak and eventually the glass breaks. Annealing will not fix this. "Micro-vibrations" may exist, but whatever stresses they create will not be remembered by the glass unless they heat the glass past the strain point. This is very unlikely to say the least.


I know Andrew Brown anneals all his cold worked pieces after cutting/polishing them, and I've seen the result of NOT annealing them soon enough. Stuff has fallen apart on his table between cutting and annealing - I can't say if it's a problem annealing would have helped or not
I can. It is indeed a problem annealing can help, but for an entirely different reason.

Have you ever looked at a 1" clear glass rod under a polariscope? It is full of stress because they do not anneal manufactured rod. But the rods will not break from this stress because the stress follows the contours of the surface of the rod perfectly. The lines of stress are parallel to the surface. If you then work the tip of the rod in a flame, you change the lines of stress. At the point where the heat stopped, the lines of stress break away from the straight parallel line and bend out at a 90 degree angle to the surface. When this glass cracks, it cracks at the point where the lines of stress reach the surface of the glass.

Have you ever looked at a paperweight with many inclusions under a polariscope? Even though it has been annealed, it is still full of stress. It looks like an onion with lines of stress mimicking the outer shape of the weight. This is because of the many different kinds and viscosities of glass inside the weight. As the weight falls to room temperature, the different glasses are all pulling on each other because of these different viscosities creating stress no matter how long you anneal. But, like the clear glass rod, as long as this stress is "parallel" to the surface, it will not cause the glass to break.

Andrew then takes one of his pieces and slices off a part of the surface and polishes it to make a window into the interior. In doing so, he cuts through the existing parallel lines of stress bringing them to the surface where they are capable of compromising the glass. Re-annealing the cold-worked piece re-arranges the lines of stress so that they are once again parallel to the surface. Note that his cold working does not introduce new stress into the glass. He actually exposes already existing stress. This is an important distinction.

Glass is mysterious stuff. No one really understand all of its intricate mechanical properties in all applications. But we do the best we can to understand what is happening by starting with basic concepts that apply to all situations. Remembering the concept of "elastic vs plastic" is one of the most important of all.

- RAM

[SNYD]

Thanks Robert, Really good info. Thanks for your input.

[jr23]

What a little gem this thread turned out to be.

[lucidvisions]

I knew you could explain it so much better. Thanks Robin! Your info about Andrew's pieces and why and what happens when reannealed makes complete sense now.

Josh

[magism]

Great read. Thanks so much.

[BORO]

This is great info..

It was a current topic between myself and a shop mate, so glad I found this thread.

[oHIGHo]

I've looked at pieces in the polariscope with a ton of stress and after coldworking you can alleviate some of it. The opposite effect has taken place too lol

[glass charlie]

Great info thanks