Why is picture frame glass used? For several reasons:
- To protect the picture from dust and dirt
- To protect the picture from ultra-violet (UV) light
- To protect the picture from heat (near infra-red)
- To protect the picture from humidity
There are various types and thickness of glass:
- Regular clear glass between 2.0mm and 2.5mm in thickness
- Extra clear glass, which is iron-free and comes in 2.0mm thickness only
- Laminated glass, which comprises two sheets of glass with a polyvinyl butyral (PVB) layer between them. The PVB binds the glass together and makes it shatterproof.
- Acrylic glass, used for large frames
There are also treatments for glass:
- Non-glare etching to reduce reflection
- Non-reflective coatings in one or more layers
Before choosing the type of glass for the picture, select its position for hanging. Is it near a window that is often open to the sun? If so, a good UV screening glass is vital, as the picture will deteriorate rapidly otherwise. Is the picture going to hang in a kitchen or bathroom? It will need protecting from steam and humidity. If the picture will be facing a light source, such as a window, it will benefit from having a non-reflective glass over it.
What is sometimes called ‘museum glass’ is probably the best solution for framing all pictures; however, it is the most expensive. It is two sheets of glass bonded together with a high quality UV protective layer. It will allow 97% of the light through to the picture, whilst blocking 99% of UV light. Only 1% of light is refracted, so the effect is as though the glass is invisible and one is looking at the picture unadorned. This glass is susceptible to finger prints and dust, so one should be sure to keep it very clean.
It is possible to cut your own glass to size, as framing with high quality non-reflective UV protective glass can be expensive through a professional framer. However, it is not easy to buy the glass at wholesale prices, and the mark-up on sheets of specialist glass is high.
It might be possible to talk a professional framer into selling a box of glass to you at less than retail price, so ask around. Look at the Internet for wholesalers nearby, and look at the do-it-yourself websites for more information. Many of these have Q & A forums where people experienced in doing their own framing with picture frame glass give tips.