How do additives affect the properties of glass?

..........just as the boiling point of any liquid INCREASES in the presence of dissolved solutes. Glass blowers are of course aware of this, and they may purposefully add materials to change the workability and properties of the glass. Glass manufacture is of course a huge industrial concern; while glass is fragile (armoured glasses are possible) it is largely chemically inert, and thus is it the premier material for containing liquids and gases. Also of course, glass is transparent; you can see the contents of the vessel. And glass is plastic...a glass blower (or a talented amateur) may purpose make a glass vessel for a specific experiment.

If you work or study in a chemistry department it is a good idea to get the glassblower on side; i.e. meet him, greet him, get to know him. He is undoubtedly the most important technician in a chemistry department, and your research will depend on the instruments he makes for you. AS a tip, any glass that you submit to the glassblower for repair or modification must be SCRUPULOUSLY clean; the glassblower will insist on this anyway but he will appreciate not having to tell you.

PS I did refer to the #"glassblower"# as a #"he"#, which is a bit sexist, and in fact I met a good female glassblower recently. She told me that the profession is still male-dominated, and her training and apprenticeship were hard...…

PPS Just to add that the scientific revolution in the WESTERN world, as opposed to the Eastern world of China and Japan possibly owed to glass... In the western world, wine was the preferred drink. And of course, you brew wine or beer, and a clear glass vessel allows you to appreciate its beautiful colour, as well as its flavour. The skills of the glassblower who made the bottles and wine and beer glasses thus lent themselves to the later manufacture of precision, transparent glass instruments including lenses, beakers, retorts....

Contrast this with the Eastern world, where tea was the social drink. Tea is still served in porcelain vessels, and while porcelain may be beautifully crafted by a potter, it is too all intents and purposes non-transparent, and THUS WHOLLY UNSUITED as a scientific instrument.