Our Fine Art Trade Guild calls it 'Cotton Museum board. Below is the bumphf from their site, I was going to just add a link - but it goes on about all the different types of board, right down to acid laden stuff. So, sorry for the long-winded post.
On a personal note, even after all this - the best quality 'Museum' boards, like most conservation boards, protect artwork by doing nothing. Artcare boards, made from cotton or not, outperform them, so why can't they be put in the same bracket - or even one above such as 'ACTIVE MUSEUM'
It's all conservation to me. But anyway .....
Test references are given in brackets
1. Cotton Museum Board - Only boards that meet the Cotton Museum Board Standard can be used for museum level framing, but these can also be used for conservation level framing.
1.1 Pulp
1.1.1. It must be made from 100% cotton fibre; this includes all facing and backing papers.
1.1.2. It must not contain post consumer waste. (TAPPI T 401; Graff ‘C’ Fibre Analysis –IPST)
1.1.3. Pre consumer waste must be of a known, identifiable and consistent quality.
1.1.4. Impurities - The product shall be free of metal particles, waxes, plasticisers, residual bleach, peroxide, or other components that could lead to the degradation of paper and artefacts in contact with, or in the immediate vicinity of, the cotton museum board.
1.1.5. The product shall contain less than 0.0008% of reducible sulphur (TAPPI T 406)
1.1.6. Free Metallic Impurities – Iron shall not exceed 150 ppm and copper should not exceed 6 ppm (TAPPI T 266)
1.1.7. The stock must be free of optical brightening agents.
1.18 Any use of the term ‘Rag’ must relate to product made only from cotton fibre pulp or virgin cotton linters (see glossary). Its use in product specifications must be avoided.
1.2 pH
1.2.1. Unbuffered museum board will have a pH in the range of 6.5 to 7.5 (TAPPI T 509). When used for mounting for display of photographic prints it must pass the Photographic Activity Test. (ISO 14523-1999 or ANSI/APM IT9.16-1994) - See Introduction for special notes on photographs
1.2.2. Buffered museum board will have a pH in the range of 7.5 – 9.5 (TAPPI T 509). When used for mounting for display of photographic prints it must pass the Photographic Activity Test. (PAT ISO 14523-1999 or ANSI/APM IT9.16-1994) -
See Introduction for special notes on photographs.
1.2.3. Any use of the term ‘acid free’ must be supplemented by the glossary definition. Its use in product specifications must be avoided.
1.3 Fillers and Alkaline Reserve – Manufacturers should include the list of additives on the Museum Board label, except where the filler is used exclusively for the purpose of buffering.
1.3.1 Fillers can only be allowed where not detrimental to the permanence and performance of the product.
1.3.2. Alkaline reserves (ASTM D4988-89) and activated carbon/charcoal may be used as fillers (ASTM D4988-89). Alkaline reserves will constitute a minimum of 2% and a maximum of 5% of the total volume by weight.
1.3.3. Calcium, zinc and magnesium carbonate are allowable alkaline reserves.
1.3.4. Zeolites are allowable as fillers when used with the appropriate alkaline reserve and should be clearly declared in the product specification. The Guild acknowledges these new products have been widely accepted as inert; they remain under careful scrutiny.
1.4 Sizing
Only neutral or alkaline sizing must be used.
1.5 Colour
Dyes and/or pigments must be non-bleeding, lightfast and resistant to abrasion.
1.5.1. Bleeding - (test based on TAPPI T 475) Any dye or pigment in the board shall show no bleeding when soaked in distilled water for 48 hours at room temperature while held down with a weight against a sheet of white bond or blotting paper.
1.5.2. Lightfastness – (BS1006:97) The colour of the stock must not register at less than 5 on the Blue Wool Scale, nor change more than 5 points of brightness (TAPPI T 452) after exposure in Sunlighter 11 for 96 hours, or when exposed in a standard fadometer for 36 hours (ASTM D3424).
1.5.3. Abrasion – (CROCK Test, BS1006 X 12.1978) Alternatively, an empirical and subjective test is to apply one pound (453gm) of pressure, rub the surface of the board back and forth with a white muslin cloth about ten times. Nothing should transfer or rub off.
1.6 Lamination Adhesives
1.6.1. Any adhesive used shall have a pH of 7 – 9.5.
1.6.2. Any adhesive used shall not soften or run under normal conditions and use.
1.6.3. Any adhesive used shall not discolour, or fail, causing delamination over time.
1.7 Moisture Content
The equilibrium moisture content of the product should be in the range between 4 and 8% at the time of manufacture
1.8 Markings
No markings (product ID, bar code etc.) on the board itself.
1.9 Thickness
Thickness will be described in metric units. Tolerance: plus or minus 7.5%. Stating imperial equivalents (inches) is acceptable additional information. (TAPPI T 411)
1.10 Board Dimensions
1.10.1. Dimensions will be expressed in metric units – millimetres (mm) or centimetres (cm). Stating imperial equivalents (inches) is acceptable additional information.
1.10.2 Tolerance – – zero minus tolerance, 3mm plus tolerance
1.10.3 , squaring and tolerance for length and width must comply with ASTM D5625.
1.11 Quality Control
1.11.1. The product should be free of fingerprints, dirt, scuffs, bubbles, knots, and other abrasive particles.
1.112. Edges should be cut square and clean.
1.113. The product should be free of bent corners and delamination of plys and surface papers
1.114. The product should have an acceptable level of flatness and be in equilibrium with ‘normal’ conditions.
1.12 Packaging
1.12.1. The product should be packaged so that it will maintain the moisture content during transit that it had at the time of manufacture.
1.12.2. The product should be packaged securely for transit.
1.12.3. Packaging will clearly indicate the content quality – Cotton Museum – and a batch number, size and thickness of the board.