Lignin-free mat board is made from 100% cotton rag or from chemically purified wood pulp [1]. Acid-free is not the same as lignin-free [4]. Alpha-cellulose is a term defined in one supplier glossary as a purified polymer derived from wood pulp; that glossary says products using it are not automatically acid-free [6]. When you specify board, ask for lignin-free and check whether buffered or unbuffered suits the artwork.
Buyer guide
What lignin-free and alpha-cellulose mean in matboard
Lignin-free matboard is made from 100% cotton rag or from chemically purified wood pulp from which the lignin has been removed [1]. Lignin breaks down into acid compounds as it ages [5], and NEDCC advises avoiding lignin-containing mat boards [2]. This guide explains lignin, alpha-cellulose, acid-free and cotton rag so you can read a board specification.
What lignin is and why it matters in a mat
Lignin is a component of plant cell walls [5]. A research article in the Journal of the American Institute for Conservation describes lignins as complex polymers that are amorphous and three-dimensional in structure [4]. The same article, citing Biermann (1996), gives lignin content in North American woods as about 18 to 25 percent in hardwoods and 25 to 35 percent in softwoods [4].
For framing, the concern is what lignin does over time. A conservation glossary from the Missouri State Archives describes it as unstable, light sensitive, and breaking down into acid compounds as it ages [5]. NEDCC advises avoiding any lignin-containing paper-based mat boards [2].
One honest caveat: the JAIC authors note that some researchers suggest lignin may enhance paper permanence by acting as an antioxidant, a point the article presents as still open to debate [4].
How pulping affects lignin in wood-pulp board
Not all wood-pulp board is the same. The JAIC article says that pulping processes that remove or reduce lignin use a chemical reaction to dissolve it, while groundwood and thermo-mechanical pulping leave most of the lignin in the pulp [4]. It adds that the more lignin is removed, the smaller the yield and the greater the final paper cost [4].
Paperboard made with groundwood pulp therefore keeps most of its lignin [4].
Acid-free is not the same as lignin-free
This is the most common mix-up. The Missouri State Archives glossary says acid-free indicates a pH of 7 or above, but adds that this may only have been true at the time of manufacture [5]. The JAIC article states plainly that acid-free does not equate to lignin-free, and that pH cannot be used as an indirect method of determining lignin content [4].
It also notes that some producers add buffers to paperboards made with acidic groundwood pulps [4], so a board's pH reading can be misleading. A pH number on a label is therefore not enough. Look for the words lignin-free as well, and ask the supplier what test supports the claim.
What alpha-cellulose means on a label
Source [6], a supplier glossary, describes alpha-cellulose as a highly stable, purified polymer derived from wood pulp and says it is used in both archival and non-archival mat boards. It says only purified alpha-cellulose gives the chemical stability archival standards require, and that archival alpha-cellulose mats are often buffered, but that lower-cost decorative mats may use alpha-cellulose mixed with lignin-containing fibres [6]. The word alpha-cellulose on its own therefore does not tell you which kind of board you are getting. Ask whether lignin has been removed and whether the board is buffered.
The same glossary adds a caution that matters for buyers: alpha-cellulose products are not automatically acid-free [6], and only products certified lignin-free and buffered should be considered safe for valuable works [6]. The only definition cited on this page comes from a supplier glossary [6], so check any alpha-cellulose claim against the board maker's technical data.
Purified-pulp board versus cotton rag board
The Library of Congress lists both routes for matboard [1]. They differ in what the board is made from, and in how strictly some conservators specify them.
- Cotton rag: NEDCC recommends 100% cotton rag mat board for every window mat, and for every layer of a layered mat [2]. The Canadian Conservation Institute (CCI) notes that manufacturers describe conservation matboard as 100% rag fibre, either buffered (pH 7.5 to 8.5) or unbuffered (pH 7) [3].
- Purified wood pulp: CCI describes matboard from highly purified wood pulp, buffered to pH 8.5, as an acceptable and more economical alternative to rag [3].
- Buffering: According to NEDCC, alkaline buffering, typically with calcium carbonate, is found in most mat boards, but unbuffered boards exist for sensitive photographic materials such as cyanotypes, some albumen prints and many color prints [2].
The table below sets the two routes side by side. For valuable or irreplaceable pieces, follow the conservator's advice. For more on mounting, see our guide to conservation matboard and mounting for framed prints.
| Point | 100% cotton rag board | Purified, lignin-free wood-pulp board |
|---|---|---|
| Made from | Cotton rag fibre [2][3] | Wood pulp with lignin chemically removed [1] |
| Library of Congress | Accepted option [1] | Accepted if chemically purified and lignin-free [1] |
| Conservation view | Advised by NEDCC for window mats [2] | CCI: "an acceptable, more economical alternative" when buffered to pH 8.5 [3] |
| Buffering | Buffered pH 7.5 to 8.5, or unbuffered pH 7 [3] | Buffered to pH 8.5 in the CCI example [3] |
Guides use slightly different wording. Check the board maker's technical data for the exact product.
How this applies when you work with us
Share your specification at enquiry; the quote confirms what is possible, minimum order and lead time. If mat board specification matters for your range, say so in your enquiry and we will tell you in the quote what we can supply. See how pricing, minimums and lead times work or contact us and we reply within 1 business day.
Further reading
Further reading
- Matting and Framing, Library of Congress. loc.gov
- 4.10 Matting and Framing for Art and Artifacts on Paper, Northeast Document Conservation Center (NEDCC). nedcc.org
- CCI Notes 11/5 Matting Works on Paper, Canadian Conservation Institute. canada.ca
- Effects of Enclosure Papers and Paperboards Containing Lignins on Photographic Image Stability, Journal of the American Institute for Conservation, 41(3), pp. 279-290 (Burge, Reilly, Nishimura, 2002). cool.culturalheritage.org
- Conservation Services Terms, Missouri State Archives. sos.mo.gov
- Glossary: alpha cellulose, Web Picture Frames (supplier glossary). webpictureframes.com
FAQ
Questions buyers ask
What does lignin-free mean for mat board?
It means the board is either 100% cotton rag or wood pulp that has had its lignin chemically removed [1]. The Library of Congress lists both for matboard [1], and NEDCC advises avoiding lignin-containing paper-based mat boards [2].
Is acid-free mat board automatically lignin-free?
No. Acid-free is usually taken to mean a pH of 7 or higher, and that may only have been true at manufacture [5]. The JAIC article states that acid-free does not equate to lignin-free and that pH cannot be used to determine lignin content [4]. Some producers add buffers to paperboards made with acidic groundwood pulps, so a pH reading can be misleading [4]. Ask for lignin-free as well.
What is alpha-cellulose mat board?
One supplier glossary says alpha-cellulose is used in both archival and non-archival boards, that lower-cost decorative mats may blend it with lignin-containing fibres, and that products using it are not automatically acid-free [6]. The word on a label does not settle the quality question. Ask whether lignin has been removed and whether the board is buffered.
Is cotton rag board better than purified wood-pulp board?
NEDCC advises 100% cotton rag board for window mats [2]. CCI says highly purified wood-pulp matboard buffered to pH 8.5 is an acceptable and more economical option [3]. The Library of Congress lists both routes [1]. Follow a conservator's advice for valuable works.
What pH should a conservation mat board have?
The Library of Congress describes matboard as pH-neutral or slightly alkaline, giving pH 8.5 as the figure [1]. CCI gives pH 7.5 to 8.5 for buffered rag board and pH 7 for unbuffered rag board [3]. These figures come from different organisations and describe different board types, so confirm the exact value in the board maker's technical data.
Should I always choose buffered board?
Not always. NEDCC notes that most mat boards carry an alkaline buffer, but unbuffered ones exist for sensitive photographic materials such as cyanotypes, some albumen prints and many color prints [2]. Check what suits the artwork.
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