Reference
Materials compared
One row per material that can go inside a frame: what it is, what it does, where it is the wrong choice, and who says so. Rows where publishers disagree say so in the row.
Read the where it is wrong column before the what it does column. Most of the damage found in an old frame came from a material that was perfectly good somewhere else in the package. The words explains why the adjectives on the label are not in this table.
| Material | What it is | What it does | Where it is the wrong choice | Who says so |
|---|---|---|---|---|
| Cotton rag board | 100 percent cotton fiber in core, facing and backing, from linters rather than textiles | The top grade. The trade specification requires it at its highest level, minimum 1100 microns, and sets limits on sulphur, iron, copper and brighteners | Nowhere, except on a budget where the piece is reprintable | A UK trade body's mountboard standard; a practitioner supplement hosted by a national library |
| Alpha cellulose board | Chemically purified, lignin-free wood pulp, often sold as conservation board | The honest floor for anything irreplaceable. The trade specification asks for at least 84 percent alpha cellulose at its second level | Where the piece is a traditionally processed photograph and the board is buffered, in one view | The same two |
| Colored surface paper over a groundwood core | A decorative facing laminated over poor-quality board | Nothing good. This is the board that leaves the brown window line | Everywhere a piece will stay. A federal leaflet calls the result acid mat burn and names this construction as the cause | A federal leaflet; a conservation institute |
| Buffered board | Board with an alkaline reserve, usually 3 percent to 3.5 percent calcium carbonate | Neutralizes acids as they form. A federal leaflet asks for pH 8 to 8.5 for paper documents | Alkaline-sensitive processes. A professional wiki says unbuffered is required for cyanotype and dye transfer; a federal leaflet says buffered is not recommended for color images, cyanotypes or albumen prints | Three publishers, three lines; see Buffered or unbuffered |
| Unbuffered (photographic) board | Cotton board without calcium carbonate added | For alkaline-sensitive materials: reactive metals, protein-based textiles such as silk or wool, and photographic media such as gelatin or albumen | Where an alkaline reserve would help, such as brittle prints on acidic mounts | A practitioner supplement; a professional wiki; a conservation center |
| Ordinary picture framing glass, 2.5 mm | Clear float glass | Cheap, rigid, non-static, dimensionally stable. A published table gives 1.2 pounds per square foot | Where it would fall on someone; above about 48 by 68 inches, which is one maker's largest sheet; over friable media without a spacer | A trade association's weight table; a maker's own size and suitability lists |
| Ultraviolet-filtering glass | Coated or treated float glass | Makers claim up to 99 percent of 300 to 380 nanometres. A trade threshold allows the label at 97 percent | As a substitute for controlling light. Independent testing of museum-targeted glass filters averaged 83 percent with a 14 point spread | A maker's product pages; a conservation institute's 2012 testing |
| Etched non-glare glass | Acid-etched surface | Diffuses reflections, with the haze clearing only in contact with the artwork | Work on paper, because conservation framing requires a gap and the haze does not clear across one | A conservation institute; a professional wiki |
| Ordinary acrylic | Cast or extruded acrylic sheet, specific gravity 1.19 | About half the weight of glass, does not shatter, available much larger | Against friable media. A preservation center says conventional acrylic carries a strong static charge and must never be used for pastels, charcoal or light tissue-like papers | A preservation center; a conservation institute |
| Anti-static ultraviolet-filtering acrylic | Acrylic with an anti-static and usually anti-reflective coating | The professional wiki's answer for friable media, with at least an eight-ply mat's worth of space. One maker publishes a static decay of 0.01 seconds under a federal test method | Where it will be scratched or cleaned often: a maker publishes a haze change of 11 percent after ten abrasion cycles | A professional wiki; a conservation center; the maker |
| Laminated glass | Two sheets with an interlayer | Holds shards if broken; a true vapor barrier; carries published safety classifications. A maker recommends it for parchment, albumen and panel paintings | Weight; it is heavier again than plain glass | A maker's product sheet; a conservation institute for wrapping large glazed frames |
| Japanese paper hinges with wheat starch paste | Long-fibered tissue, water-torn, with cooked starch paste | The sanctioned adhesive attachment. Reversible, and deliberately weaker than the artwork so it fails first | As a first attempt without practice. Every publisher that describes it says to practice on scrap paper first | A national library; a conservation institute; a federal leaflet; a professional wiki; the trade specification |
| Non-adhesive paper corners | Folded from unbuffered alpha-cellulose paper | The one method a household can execute correctly, with no adhesive touching the object | Brittle or large objects, where a federal leaflet says corners are inappropriate; unmounted albumen prints, which sag | A federal leaflet; a professional wiki |
| Plastic film corners | Polyester corners, usually with an acrylic-adhesive tape | Convenient and widely sold | Publishers disagree. A professional wiki says photo corners of any plastic should not be used with photographs, because they may scratch or emboss binder layers; a federal leaflet and the national archives allow inert plastic film corners | Three publishers; see The three disagreements |
| Polyester strip supports | Strips laced through slits in the back mat and taped behind | Non-adhesive support for sturdy objects, snug but not taut | Friable media; very brittle objects, where polyethylene is suggested instead; across the image, where differential fading has been observed | A federal leaflet |
| Any tape on the object | Pressure-sensitive, gummed, linen, or sold as archival | Nothing this manual will endorse | On the object, always. A professional wiki says tape should never be applied to the paper object when matting and framing | A professional wiki; a conservation institute; a national library; a state archives |
| Acrylic-adhesive tape, inside the package | Named double-sided and mending tapes with acrylic adhesives | Accepted for mat construction, taping frame rabbets, sealing mat packages and attaching corners, because acrylic adhesives have not been observed to degrade as rubber-based ones do | In direct contact with the object | A professional wiki |
| Water-activated gummed linen tape | Cloth tape activated with water | Joins the window mat to the back mat along the long edge | On the object. A federal leaflet puts the exception in its own capitals: these tapes are used only on the matboard | A conservation institute; a federal leaflet; a national library |
| Dry mounting | Heat-activated adhesive bonding the print to a board across its area | Produces a perfectly flat print | Anything you would not replace. A conservation institute says it is, practically speaking, irreversible, and that the maker's claim about reheating to dismount is not safe for prints | A conservation institute; a preservation center |
| Four-ply rag backing board | Cotton board behind the back mat | Stable, inert, the default on anything small | Large or heavy pieces, where it will not stay flat on its own | A conservation institute; a national library |
| Twinwall corrugated plastic | Fluted polypropylene sheet, 4 mm or 6 mm | A moisture barrier, more puncture-resistant than corrugated paperboard. A conservation institute ranks it first for buffering humidity behind a canvas | Where a non-archival coating has been applied, which a professional wiki notes some products carry | A conservation institute; a professional wiki |
| Acid-free corrugated board | Lignin-free corrugated paperboard, 1/8 or 1/4 inch | Light, cheap, an outer backing | In uncontrolled environments: a professional wiki reports it expanding more than non-acid-free cardboard, in one case pushing a 30 by 40 inch framed piece off the wall | A professional wiki; a national library |
| Paper-faced foam board | Polystyrene core between paper facings | Publishers disagree. Two conservation-institute notes list it among boards to use; a preservation center says not to use any type of foam board | In contact with an object. A professional wiki reports paper-faced versions yellowing within months from degradation of the core, and says it may be used as an additional outer backing for travel | Three publishers; our default follows the wiki |
| Hardboard (Masonite and similar) | Compressed wood fiber panel | Rigid and cheap | In contact with anything. A conservation institute names it among materials not acid free that may migrate acids and resins; a professional wiki notes it has been reevaluated in light of research on formaldehyde emissions | A conservation institute; a professional wiki |
| Ordinary corrugated kraft cardboard | Brown corrugated packaging board | Nothing, inside a frame | Everywhere. Groundwood and lignin generate acids rapidly | Every conservation publisher in this research |
| Raw wood, including slat backing | Unsealed timber in contact with the package | Nothing good | In the rabbet unlined, and as a backing: a preservation center warns that wooden slat backing boards will over time burn a strong wood grain pattern into paper-based material | A national library; a preservation center |
| Barrier film in the rabbet | Aluminum or polyester tape with acrylic adhesive, lining a wood rabbet | Stops acids in the wood moving into the mat package | Nowhere; it is cheap and it is usually skipped | A national library; a preservation center |
| Sealed package | Glazing, the matted work, acid-free backing and polyester film, sealed at the edges and dropped into the frame | Buffers temperature and humidity swings and keeps out dust and pollutants | Where it is built as a sealed frame: a professional wiki says sealing the back and edges can trap humidity or slow its release, and that the safer solution is a sealed package inserted into the frame | A professional wiki; a preservation center; a conservation center; against two conservation-institute notes |
| Dust cover | Paper or spunbonded sheet across the back of the frame | Keeps dust out of the frame cavity; carries the dated label | As a substitute for a backing board | The trade specification; a preservation center |
| Acid-free glassine as a cover sheet | Smooth translucent paper | Often suggested as interleaving | As a cover sheet: a preservation center says it becomes acidic over time and distorts with humidity, and research reported on a professional wiki found glassine and buffered tissue both yielded poor results for interleaving photographs | A preservation center; a professional wiki |
How to read this table
- Rows marked Refused are not a matter of budget. They are the four or five materials every conservation publisher in this research names, plus tape on the object.
- Where publishers disagree, both positions are in the row. This manual gives one default and puts the full disagreement in a Go deeper block on the relevant chapter page.
- "Who says so" names the kind of body, not a brand. The resource library lists each source with its publisher and what it covers.
- Take the row names to a counter. A material named by what it is made of is a material you can hold a quote to; an adjective is not.
Limits
This table summarizes published guidance about materials in general. It has not seen your piece, it is not a specification, and it does not price anything. Where a maker's figure appears it is the maker's own claim about its own product, which is a product fact and not a conservation finding.