The Science of Glass workshops-in-murano-italy

Formers Fluxes Stabilizers Typically silica (SiO 2 ) in the form of sand. Melts at a very hot temperature. An alkali to lower the temperature of viscosity. Sodium carbonate plant ash (Na 2 CO 3 ) Make the glass strong and water resistant (glass is polar without it) Limestone (CaCO3) Three Main components:

Tetrahedral Molecular Geometry The tetrahedrals form a network of chains which the sodium disrupts. Pollard, Archaeological Chemistry, 2008 ( ) Bridging oxygen (no charge) Non- Bridging oxygen (negative charge)

Physical characteristics The structural rigidity of a solid but the random molecular arrangement of a liquid (no melting point – Supercooled liquid)

Paul, 1990, Fig. 102 Crystal transitions from liquid to solid. Melting point of crystal. Glass has no melting point and no distinct transition from liquid to solid.

Why does glass crack when it goes quickly from hot to cold? Glass has a high thermal expansion coefficient (it expands a lot when heated because of its loose structure (compared with other solids)

Additives (optional) Boron makes glass heat resistant (lab glass, cooking glass etc.) Lead makes glass shiny – crystal Colors - different colors can be added to the glass by the addition of powdered transition metal oxides. Cobalt – blue Copper – blue/green Chromium - green Titanium – yellowManganese – purpleNickel - gray

What are some of the considerations of glass blowing? Heating – glass has no distinct melting point so temperatures are defined by viscosity. The flux lowers the temperature at which glass becomes workably viscous. Holloway, 1973, 19

Popping air into glass – small amounts of air are introduced and the heat expands Cooling – thicker parts of glass stay hotter longer than thinner parts of glass so the glass must be cooled very slowly through a process called “Annealing”

What is the history of glass? 2000 BC First examples of glass from the Mesopotamians. 50 BC Romans invented glass blowing which made the process faster and more affordable needed colored glass for stained glass windows and used beech ash as the flux, which is water soluble. (Makes cleaning very difficult). 1800s- Made stained glass windows by painting on layers of transition metal oxides in borax. Borax is also water soluble which makes the colors dissolve away with cleaning. glass/cleaning-stained-glass.htm

c=frontcover#v=onepage&q&f=false information/about+pilkington/education/chemistry+of+glas s.htm Blown-Glass-Pumpkins.html GLASSb.gif asEng.pdf oregon/