Glazing is the protective covering used in framing artwork and items. The two most common glazing materials are glass and plastic. Not all artwork needs glazing, oils and acrylics for instance get protection form the layers of varnish on them.
The primary function of a glazing material is to provide the items with protection. However, both aesthetic and conservation considerations should influence the choice of material and framing technique. When choosing a glazing material, it is important to be familiar with the distinct types of glass and plastic and with the properties of each. Your bespoke framer will guide you through the options and show you samples.
The protection comes from the glazing forming a barrier to the environment. It minimises physical damage, ingress of pests (insects) and airborne contaminants such as dust. It buffers the artwork from extreme fluctuations in temperature and relative humidity.
It is important to have a small breathing air space inside the frame between the item and the glass. This allows condensation to form on the inside of the glass and not on the artwork where it will cause damage and potentially mould to grow. It helps avoid image transfer and staining. This space is achieved by use of a window mount or spacers that fit into the frame rebate.
Both types of glazing have advantages and disadvantages.
Glass is scratch resistant and rigid. But it breaks easily and is heavy.
Plastic (styrene, acrylic) is easily scratched and may bow. It does not break and is much lighter than glass.
I use glass for most frames. The exception is when safety is an issue or if a large piece of glazing is needed, over 1m x 1m. The weight and size of handling this size glass is difficult (unless you have arms like Mr Tickle that it).
Both types of glazing are also available in range of thicknesses and grades.
Standard glazing provides the basic protection. It will keep the items damage and dust free. It does not protect from damaging ultra violet rays.
Ultraviolet radiation (UV) causes weakening and yellowing of paper and other organic materials. UV may also affect media, causing colours (dyes and pigments) to fade or change.
To minimise such damage there is conservation grade glazing. It has a optical coating that filters 98% of UV rays slowing the damage from light.
For the best optical experience anti reflective glazing is recommended. A special coating reflects less than 1% of light so you can appreciate the framed item from all angles and distances much better. It come with 70% or 92% UV filtering. Its the glazing on the right in below image (sorry not the best quality image).
For the ultimate optical and UV filtering glazing then the highest specification is museum grade glazing. This combines UV filtering with the antireflection properties.
The type needed for your frame will be dependent on the item being framed, your visual preference, conservation considerations and the cost.
I would strongly recommend conservation glass on the majority of items, especially delicate water colours, photos and old brittle works on paper. Ask me about all of them.
