Why write about picture frame backing boards? Truth be known, we were scratching for ideas for this month's post. We asked the lads for suggestions for a new post but most told 
us that they felt that we must have written just about everything there is to know about picture frames. And that seemed to be so until someone asked about backing boards, had we ever written anything about them? The answer was in the negative, and do, here we go, let's discuss backing boards, the kinds used in picture framing to make picture frames. To begin with, and so far as the picture framing occupation is concerned, backing boards, backer boards, back boards, backs and and backings are all synonyms of the samecomponent, the backing boards at the rear of photo frames, picture frames and poster frames.
We can the progress as to the function of this component, or picture frame part. Our web page Picture Frames Parts Names lists all the main components of a picture frame, including the backing board which is photographed and includes a brief description. Nevertheless a fuller and more detailed explanation of this component is apropos.
We will begin by describing the purpose and functions of this picture important, but often unseen and unappreciated frame part. Perhaps the foremost feature and advantage is that it is a hard, and stiff surface against which the artwork, window mat (if any) and glass rest.
Without it, all these parts would, more, or less, tend to fall out of the frame. This strong, straight, thick and rigid surface also forms and acts as a barrier against insect entry, arachnid nesting and other hexapod invertebrate intrusions as well as protecting against common fumes and other household pollutants.
A backing board is always cut a little smaller than the rear aperture of the frame. How much smaller depends on the picture frame making the frame, however, we, ourselves, generally prefer 3mm. This is called a clearance and it's engineered so as to avoid the backing being or getting jammed into the frame whilst fitting up.
Thus if a picture frame's rear aperture is, say, exactly 900x600mm, we would cut the backing 897x 597 mm. That way the backing can be put inside, or fitted up, or assembled, into the frame without too much jamming into the sides, or trouble.
Backing board can be sourced form just about any material that is thin a rigid enough but here in Australia, generally come in three main types, 1) MDF ( Medium Density Fibreboard ) , 2) Acid-Free Foamboard and 3) other generic boards, papers or cardboards.
1) MDF is the most commonly used material because of its relatively low cost and popular sheet sizes availability. The material most used by picture framers comes in sheets, often 2440x1220 mm x 3mm which is easily fed into and cut down to size by special board cutting machines such as the one below:
While relatively inexpensive, MDF suffers one important drawback. Being constituted from the cellulose of wood chips it contains lignin which is highly acidic. This acid matter little in the framing of inexpensive, ephemeral, every-day, disposable art such as open-edition commercial prints and posters.
This is because any future 'yellowing" effect on the art matters little when it will replaced, discarded or disposed of in a few years as most fashion art is nowadays. However, this "yellowing" deterioration is an entirely different matter with personal, valuable or irreplaceable art. And by that, we mean any frame-able art that has even a modicum of personal, sentimental, financial or historical value.
Think of Grandfather's Army discharge certificate, Grandmother's cross-stitch or your child's preschool drawing. None are likely to command a resale value but the sentimental value we feel and bestow one them may be priceless.
Thus, these deserve to be protected against the perils and ravages of inferior materials, bad workmanship, and the passing of time. Perhaps the most damaging peril is the use of inferior backing boards such as an MDF backing.
A picture frame backing board or backboard of, or from, his wood-based material maybe fine for an el-cheapo, holiday home poster but not a all for the finer art mentioned beforehand. We can't count the number of times we de-framed a lovely Limited Edition print or an antique or original etching only to find them completely yellowed and brittle as a result of ligninic acid migration from the backing and into the paper art itself.
An example typical of the kind of damage inflicted by the use of acidic backings and other kindred materials is shown below , which incidentally, also evidences significant foxing almost certainly caused by an acidic window mat.
2) Acid free Foamboard, also known as, Foamcore. This is also a popular product and a much cleaner than the preceding MDF backing board material. It is mostly used by photographers, collectors, curators and artists and for original art, such as watercolours, pastels, gouaches, etc and fine art such as etchings, Limited Editions, lithographs, etc.
The most popular thickness, 5 mm, is relatively strong, lightweight, of high-density, PH-Neutral and Acid Free with clean, even, smooth, laminated surfaces. It is typically constructed in three layers. The two outermost ones are white, PH-neutral, clay-coated paper while the inside one, or inner layer, is polystyrene foam. Often it is sold in pre-cut standard sizes as per our A2 White Foamboard sheets packs below:
Alas, it suffers from two serious drawbacks. The first is the cost, roughly 2 to 3 times x m2 than the cost of MDF sheets. The second is that, unlike MDF, it cannot be easily wet-mounted. Wet-Mounting ( see Picture framing wizardry and the secrets of mounting ) being the quickest, most economical and most reliable of all mounting methods cannot be easily replaced or substituted and it is the cornerstone of most commercial picture frames and industrial picture framing.
3) Perhaps one of the most egregiously unsuitable backing materials are cardboard packing boxes off-cuts, as shown below. These common packing boxes are made of the cheapest possible untreated pulp material and are pretty much guaranteed to be replete of acidic lignin as per the below illustration:
And while there other picture frame backing board materials ( Coreflute, Correx, pulp boards, liner boards, etc.) in circulation, the three detailed above would comprise about 95% of all backing board materials being used here in Australia.