Glass colour opaque

Conventional glass-ionomers are tooth coloured, and have a degree of translucency. This gives them reasonable aesthetics, though they are less aesthetic than composite resins, mainly because they remain relatively opaque compared with the tooth itself [218],... 

The main volume properties of polymers are colour and transparency. Both may either be inherent to the polymer or caused by additions, e.g. dyes and other additives. Most polymers do not show differential absorption in visible light and are therefore colourless. The volume properties cover a wide range from glass clarity to full opaqueness. This is also the case for the surface properties they may vary from high gloss to full dullness (matt). 

By the seventeenth century perfumes had begun to be stored in lightly blown glass bottles, and the eighteenth century saw the appearance of pear-shaped bottles in opaque white glass, decorated similarly to porcelain ware. Weight was reduced, and decorative appeal achieved by colour, cutting and applique decoration, which made perfume bottles truly treasured possessions, and worth much to today s collectors. 

Many polymers in everyday use contain fillers and colouring agents that render them opaque. The optical properties of the base polymer are thus obscured. On the other hand the clarity of optical transmission of many polymers and the fact that they are almost colourless, coupled with their low density and excellent mechanical properties, are the reasons for their use to replace glass in many applications. In other applications glass would be totally inappropriate because of its greater brittleness. Other polymers, such as the ubiquitous polyethylene, are often colourless but translucent rather than transparent. 

PMMA is available in granules and sheet from glass clear transparency through a full range of translucent and opaque colours, and is processed by injection moulding and extrusion. Sheet can be formed by all standard techniques. 

---