Why can you blow glass and not other materials?

  1. Hi. Often, when I am a tour guide at the Museum of Glass, Tacoma,WA. glassblowing shop. I get a question for which I don't have a definitive answer. I thought someone might know
    What is special about glass that enables it to be formed by blowing? Which forces are the major factors in holding the bubble together and allows it to be deformed in an inelastically.
    How is it different from other materials wax, steel, ceramics, wood, etc which do not have this ability? with respect to the blowing phenomena.
     
  2. jcsd
  3. u can blow glass when it is in the molten state ..it is light and relatively less dense.
    Remember that glass is a super cooled liquid.
     
  4. enigma

    enigma 1,817
    Staff Emeritus
    Science Advisor
    Gold Member

    Just shooting from the hip here, but I would guess it has to do with the relatively low melting point of glass combined with the ductility of the molten material.

    I guess you could, in theory, blow a metal, but they're probably too hot to get close enough to, along with probably too dense to be able to do much with human lungs.

    Again, I'm not any sort of expert in the matter - just brainstorming.
     
  5. what i meant to say was that when it is in the sort of molten state ..it is like a deformable plastic and yet dense enough to hold the air blown inside.The air bubble does not diffuse into the material.
    I heard this explanation on national geographic during one of the programs they covered regarding Ireland history and thier glass factories.

    i'm no expert either but confident of the statement as i got to observe an expert.
     
  6. Anything you see that can be injection molded can basically be blown just like molten glass; especially if it has a viscosity similar to glass. That pretty much limits it to glass, plastics, some ceramics, and some metals. And really only glass or plastics are formable under lung pressure alone.
     
  7. The glass is not molten when it is being blown (molten refers to the formation of a liquid, liquids cannot hold shape). It is still a solid, just in what's called a supercooled state. The liquid's atomic structure is locked in place within the solid from when it was originally taken from the molten state and cast/extruded to shape, but the temperature of glassblowing is not sufficient to allow for atomic rearrangement into the equilibrium solid crystal structure (devitrification).

    Silica-based glasses are covalent network oxides, and as such they have low solubility for molecular oxygen as compared to other ceramic oxides which have ionic bonding that can readily incorporate oxygen as O(2-) in its crystal structure. This is why you can perform glassblowing with air.

    In theory, you can plastically deform lots of materials using applied inert gas pressures, but the temperatures and pressure needed wouldn't make it practical in most cases.
     
  8. Borek

    Staff: Mentor

    I would say it is a (coincidental) combination of viscosity and surface tension, that just happen to have correct values in the temperatures that are easy to achieve.

    Coincidental in the sense that it just happens this particular material has them, for sure it can be explained in terms of physicochemical properties of the compounds present, there are probably other materials with similar properties (although I think we would classify them as glass as well, just because they would behave in a similar way).

    Or, to put it differently - of many materials that we can test, this one has a correct combination of viscosity and surface tension at elevated temperatures, so it was selected for blowing thousands years ago.
     
  9. Another factor that makes glass blowing possible, the low thermal conductivity, which is important so you can selectively melt parts of the glassware. Finally glass has amazing properties: it is transparent, very hard and chemically extremely stable, making it preferable over other materials that might work -- like tar.
     
  10. I think it is the transition temperature which matters, Transition temperature is the the temperature at which glass is in semi solid state as what is seen in some polymers. Metals do not have transition temperature because they have a definite melting point.
     
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