Gone are the days when the choice of picture framing glass was limited to float glass, diffused reflection and Perspex®. There are now close to 20 different types of glazing for every situation. It is the professional framers responsibility to advise on the options available and make this information as clear as possible. The main points to consider are:
UV - ultra violet rays have a damaging effect on art on paper and textiles, and while UV filtering glass can help protect artwork it cannot stop damage completely, only slow it down.
Reflection – bothersome reflections from light sources or windows can ruin the viewing pleasure of artwork, also very dark images or artwork can act as ‘mirrors’ behind normal float glass.
Clarity – If you put a piece of normal float glass on a white piece of paper you will see the colour darken slightly. This is broadly referred to as light transmission and specialist glazing is available which causes almost no colour shift.
The following information is not intended to be definitive, and by no means covers all glazing options, but will hopefully make choosing glass for picture framing a little clearer.
Float glass.
Still the most common and often used glass, 2mm thick but also available up to 6mm thick. The UV filter rating of float glass is approximately 47%. Float glass will slightly darken colours, this is caused by the iron content which gives the glass a green tinge. For pictures over 1 metre square I would suggest 3mm thick float or where weight is a issue; Acrylic.
Diffused reflection (also called non glare, matt, or non reflective glass).
This glass is etched on one or both sides to create a diffused surface that disrupts reflections caused by lights and windows. I always have this glass in stock, although it is rarely used, I would only recommend using it in very harsh lighting conditions. This glass has a matt and dull look, which causes a loss of sharpness in the artwork, this effect increases the further the glazing is positioned from the artwork so it can only be used over 2 or 3 mounts and not on deep box frames. The UV filter level is about the same as float glass although it is also available with a 99% filter.
Artglass™ - 2mm anti-reflective.
State-of-the-art manufacturing technology means Artglass™ has very low visible reflection while maintaining high clarity and accurate colour rendition. This is a practically invisible glass with outstanding clarity and minimal reflections. Firstly it has less iron content than float glass that gives maximum clarity and almost no change in the actual colours of the artwork. Secondly an anti-reflective coating is applied to the glass that almost totally eliminates annoying reflections. The UV filter level is approximately 70%. All anti-reflective glass is angle dependant, which means you get benefit of full visibility and minimal reflections up to a viewing angle of 45 degrees.
Artglass™ is my anti-reflective glass of choice, there are a number of other brands available which are similar, such as: Schott Mirogard®, Tru Vue AR Reflection Free®, Claryl®, and ClearColour® Plus.
Artglass™ UV - 2mm anti-reflective.
This glass has the same benefits as the Artglass™ anti-reflective glass detailed above, but it has the added bonus of a higher 92% UV filter that provides an excellent compromise between cost, clarity, accurate colour rendition, anti-reflection and UV protection. As above, other brands and makes are available.
Tru Vue Conservation Clear®
This is normal 2.5mm float glass but has a coating on one side which gives approximately 99% UV filter protection. It has the same reflection and colour darkening effects as float glass and a very slight surface ripple, which is only noticeable on close inspection. It is a very cost effective solution where high UV protection is required.
Tru Vue Museum Glass®
The same 2.5mm base as Tru Vue Conservation Clear® glass, with the 99% UV filter, and with the added benefit of a very effective anti-reflective coating which greatly reduces annoying reflections and makes the glass practically invisible. It is rather costly but is a very high specification glass.
Plastic glazing.
Various different types, thickness, and qualities are available, including diffused reflection and anti reflective.
I mainly use Artshield® 3mm Acrylic, which is much more scratch resistant than most plastic glazing. Artshield® acrylic is also available with a 99% UV filter. Plastic glazing is used when safety and weight are an issue. Perspex® , styrene, and clear cast acrylic are other types often used.
Laminated float glass.
Where safety is an issue, available in 4.4mm and 6.4mm thickness, a sheet of plastic is sandwiched between two pieces of float glass. Should the glazing be damaged the broken shards of glass are held in place and will not damage the artwork or the public. The plastic layer gives the added benefit of a 99% UV filter. The only negative with laminated glass is the considerable increase in weight.
Luxar®, Artglass™ Protect, and Schott Mirogard Protect® - laminated museum glass.
These are the ultimate glazing options, and are considered to be the best glazing available – 99% UV filter, laminated, anti-reflective, maximum clarity and perfect colour transmission – at a cost!
Mountboards
I use 3 types of mountboards – Whitecore, Conservation and Museum.
You may have seen some old mounts which have a brown bevel cut edge, this is caused by the lignin (tree sap) in the board fibres. Lignin is the binder which holds wood and paper fibres together. Over time lignin becomes highly acidic. This process is accelerated by heat and light. This acid then causes the board to weaken and discolour and the acid can soon migrate from the mountboard and causes damage to the artwork. I do not use this type of mountboard.
Whitecore board – Only used for non valuable and easily replaceable art such as posters, mass produced prints etc. Made from chemically purified wood pulp, free from lignin, and pH neutral.
Conservation board – made from high quality alpha cellulose, purified of lignin and containing an alkaline buffer to protect the board and artwork from acidic pollutants. This is the type of mountboard we use most often.
