Discoloration of the Laser Tube

Morning everybody,

Just a quick question from somebody who’s never owned a CO2-laser tube before… when I first got the machine, the tube was clear all the way through. Over time, the innermost glass surface (the one you can see the plasma shooting through) has started to turn some shade of coppery red, but still transparent. Is that the expected behaviour of CO2-tubes or do I need to worry?


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Are you sure that’s not just Dirt collecting on the Outside from smoke?
Have you tried cleaning it as per the GF instructions?

Mine’s that color.

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But @Jules we know your laser is never off! :wink:


A vile rumor, I assure you. :smile:


Yep - I clean it regularly when it becomes opaque :wink: - as I said, the colouration is on the innermost glass surface of the tube - I’d be really surprised if dirt got there.

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It is in a partial vacuum bouncing off copper mirrors no not a total surprise if a few copper ions get loose, though that awareness is after the facts perhaps.


The light transmission through a v. thin layer of gold is red, and I suspect this is what your seeing, rather than copper.
I believe that any internal mirror in the tube will be gold coated, but I may be wrong.
I have a tendency to work backwards from a single observation to a general theory, known in the family as one of my ‘Knickerbocker’ moments, due to a completely erroneous explanation of why ‘Knickerbocker Glories’ (tall ice cream sundaes in a conical glass) were so called.



This is true of colloidal gold such as is found in Gold Red glass but even that is very technical and does not always work, but when it does you are looking at light transmission through the colloidal particles. If you say spray gold dissolved in nitric/sulfuric acid on hot glass and burn off what does burn off you do not get a nice red like you do spraying copper nitrate and reducing it. but the red of gold and the red of copper (and the trickier red of cadmium/selenium) are all quite different reds.

Or as a famous glassblower said “there is no such thing as red” as it leans either to orange or purple but never pure. I suspect that the build up could be seen as the coppery orange red and not the red of Gold. But then I have not seen it personally.



Was looking carefully today while cleaning Puff and can see red coming in the tube as well. Definitely a copper red and not a gold red.