Glass has existed as a man made product since 3500 B.C. but true proliferation of cheap clear glass is a relatively modern development. While most middle age civilizations had access to glass in some form it was usually an impure or opaque product because clear glass production required the perfect source materials and extreme levels of heat. To make translucent glass lead was required to lower the melting point and provide the sought after clarity without modern furnace technology. Ancient glass was also notoriously fragile and expensive because in order to be transparent it had to be ground down to a very low thickness. The advanced chemical knowledge of alchemists combined with their powerful energy sources would have opened a world of possibilities.
GLASS AS ART
With easy access to a variety of metals and extreme heat sources and it would be possible for Alchemists to achieve crystal clear glass at very low cost in a huge range of vibrant colors. Simple glass products could be chased through with intricate patterns of stunning colors. Glass bowls cups and plates could replace early less sanitary wooden or clay creations. Vibrant stained glass colors could be achieved through the inclusion of specific minerals during the melting process.
ADVANCED LENS TECHNOLOGY
Crystal clear glass panels could be ground down to form early lens technology. Refracting light for a more powerful lantern or harnessing the sun as a source of heat energy would be possible. Advanced alignment of multiple lenses would allow for the creation of early microscopes and telescopes through which Alchemists could study objects beyond the range of human eyesight be they great or small.
Through an advanced process of chemically and thermally treating glass it is possible to significantly increase its strength and rigidity. This glass could be used to create large single paned windows and skylights allowing light to fill Addletownian structures. This would also allow for stronger glass vials and containers in which alchemical components could be stored. Note: Tempered glass shatters into chunks (think of a broken car side window) and not shards when broken.