From: Neon John <johngdNOSPAM@bellsouth.net> Subject: Re: evacuating glass for neon Date: Tue, 14 Mar 2000 04:27:56 EST Newsgroups: rec.crafts.glass bill wrote: > > This may be the start of a long dialogue..... > > I'm looking to fill some blown glass components with Argon/Neon. The > glass is a typical soda-lime base worked from a furnace as opposed to > borosilicate. > > What degree of vacuum will I need to achieve before bleeding the gasses > back in? It's a little more complicated than that. There is a significant amount of gas and water vapor adsorbed on the inner surface of the glass and absorbed in the glass. Proper prep for pumping requires baking while under vacuum. My process for large (larger than tubes) object is to bake under at least a 1 micron vacuum at about 400 deg for several hours, preferably overnight. If you don't do this, gases will diffuse out of the glass over time and spoil the fill. Additionally, if you plan on using electrodes, these must be heated cherry red to outgas them and to convert the electron emissive coating. We normally do that with a high current discharge for tubing but that doesn't work for large objects. The usual technique is to use an induction heater on each electrode while it is under vacuum. If you're not using electrodes (RF excitation), then the vacuum and baking requirements are more severe since there are no electrodes to getter any tramp gases. Argon by itself makes very little light. Argon with mercury makes more. Argon/mercury with fluorescent phosphors on the inside of the glass or fluorescent glass makes the most. Uranium glass is bright yellow; leaded glass as used for neon tubing glows a bluish white when pumped with argon/neon ("pumped blue" in the jargon). The other noble gases vary in color according to the pressure and excitation but none are terribly interesting by themselves. > What order of pressures of gas are required? For tubing, it depends on the size. For larger objects, typically 2-3 mm of mercury is pretty standard. Variations are possible to achieve different effects. More pressure, for example, will cause the discharge to go 'stringy" and snake around. Less pressure will make the discharge more diffuse and neon will tend to go more orange. > Any information and leads into this would be greatly appreciated. Best thing is to find a neon shop where the proprietor is interested in artistic neon. Not many are. But in a shop that IS interested in artistic neon, many of the variables that you would work out by trial and error have already been figured out. Plus the equipment is at hand. John -- John De Armond johngdSPAMNOT@bellsouth.net http://neonjohn.4mg.com Neon John's Custom Neon Cleveland, TN "Bendin' Glass 'n Passin' Gas" |