The days when the choice of picture framing glass was limited to float glass, diffused glass and perspex, are long since over. There are now many more types of glazing for virtually every conceivable situation. It is the framers responsibility to advise the client upon all of the options which are relevant to their requirement, those which are readily available and those which may take longer to procure.
The issues which a client may wish to consider are :-
Visibility – When you place a piece of float glass on a white piece of paper you will see the whiteness darken slightly. This is universally referred to as light-transmission: in addition, a green tinge will be equally visible due to the material content of the glass. Specialist glazing, referred to as ‘water white’ is available which eradicates this almost entirely.
UV – Ultra-Violet Light – ultra violet rays have a damaging effect on art, on paper and upon textiles, and whilst glass which filters UV light can help protect artwork it cannot stop damage entirely. It merely reduces the effects. However, the best of the glazing options reduce the effect to less than 20% and the very best reduce this even further to less than 2%
As a matter of principle, when positioning artwork of any value or significance, consideration should always be given to avoid, wherever possible, direct or harsh sunlight and similarly direct or harsh artificial light.
UV is present in all forms of daylight. Sunlight and clear blue skies having particularly high levels. Many artificial lights emit UV in a variety of levels ~ flourescent ~ halogen and HID (high intensity discharge) being by far the worst. Incandescent bulbs and fibre-optic lighting however are fairly safe.
Reflection – distracting reflections from artificial light sources. Windows or even shadows can demean the viewing pleasure of any form of artwork, as can dark images or artwork acting as reflectors behind normal float glass.
To attempt to provide resolutions to the annoyance and impediment of reflected light upon glazed artwork manufacturers have introduced diffused glazing and ant-reflective or, more realistically, reflection controlled glazing.
Each are described in the following paragraphs
The following information is not all encompassing, nor does it claim to be entirely definitive. By no means are all glazing options considered, but it will, hopefully, provide sufficient information to make the informed choice of glass, for the framer and for the client, possibly a little easier.
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 slightly less than 50%. Float glass will slightly darken colours. This is caused by the iron content which gives the glass a green tinge. It is nowadays possible to use ‘water-white’ glass which does not produce the same green tinge. For pictures over 1M2 I would suggest 3mm thick float or, where large size and correspondingly increased weight is an issue; Acrylic.
Diffused reflection (often referred to as 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 I prefer to use it only where the client specifically asks for it. It can be beneficial where the picture is to be hung in close proximity to a window, however 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, and this effect increases the further away the glazing is positioned from the artwork so I suggest that it should only be used over, at most, double mounts and certainly not with deep box frames. The UV filter level is about the same as float glass although it is also available with a 99% filter.
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 98+% 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.
Tru Vue Conservation Reflection Control Glass
The same 2.5mm base as Tru Vue Conservation Clear glass, with the 98+% UV filter, and also with the benefit of an effective anti-reflective diffused surface, which greatly reduces annoying reflections. This, at a significantly reduced cost of the Museum glass but, because of the diffuse outer surface, with a similarly significant reduction in clarity and visibility.
Various different types, thickness, and qualities are available, including diffused reflection and anti reflective.
Certain types of acrylic are much more scratch resistant than conventional plastic glazing. Acrylic is also available with a 99% UV filter. Plastic glazing is used when safety and weight are an issue. For instance in a gymnasium, or densely populated public buildings.
Laminated float glass
Where safety is an issue, available in 4.4mm and 6.4mm thickness, laminated glass has a sheet of plastic sandwiched between two pieces of float glass. In the event of impact, the fractured shards of glass are held in place and will not damage the artwork or the public. The central reinforcement layer provides the additional benefit of a 99% UV filter. One very significant negative to laminated glass is that it is considerably heavier than conventional options, due to the doubled volume of glass.
I will always seek to offer my prospective client the opportunity to make their own informed choice of glazing for their art; because I believe that to leave my client uninformed about the choices, is a very unprofessional approach to the design and selection process of framing.
I will never ‘pressure sell’ any product: but I will always attempt to ensure that my client is informed of all of the options available to them. Having done so, I consider that the choice will henceforth be theirs, without any further influence from myself.