Using “heat-set tissue” is an easy and quick way to mend torn paper. This commercial product is a transparent tissue coated with an inert acrylic resin. It requires heat in the form of a tacking iron to activate the resin and bond the tissue to the paper being mended. The mend can be easily removed with ethanol. This is not as strong a mend as the traditional Japanese tissue and starch paste but for circulating or small collections, it is much simpler and requires less dexterity and skill of the repairer. Also, this method precludes the drying time and care needed in a paste mend, since no moisture is introduced, Be sure to use a product that meets the standards of the Library of Congress.
Bookmakers, a commercial company that makes heat-set tissue to LC specifications, provides the following instructions:
“The temperature of the tacking iron should be controlled at 190-200 F. It is unwise to rub the bare face of the hot tacking iron directly onto the tissue when attaching it to the mending area because heat and friction attract particles of acrylic onto the face of a fresh tissue mend . To avoid this effect, a thin piece of Japanese paper, silicone release paper or white polyester fabric can be used between the face of the iron and the heat-set tissue. For best results large mended areas should be pressed in a heated platen press for at least 8 seconds, using a temperature of 180 F at the surface of the mend. For small tear mends, hand pressure with the hot iron is usually sufficient to achieve consolidation.”
To repair a running tear: Tear a narrow strip of heat set tissue. The tissue need not be much wider than the tear (1/8″ or so is usually wide enough). The tissue is torn rather than cut for two reasons: a torn edge repair is less visible than a cut edge; and a torn edge has some fiber extension which gives better adhesion. Position the tissue over the tear, let part of the tissue overhang the edge of the page; cover with a piece of release paper and use the tacking iron to adhere the strip. The overhang can now be turned over the edge of the page and adhered to the verso. That seals the edge of the tear.
For mending lacunae [a hole in the paper], two patches slightly larger than, yet conforming to, the contours of the missing area should be shaped in the following manner: place a sheet of polyester film over the lacuna to protect the document while you are working; place the tissue over the film. With a needle, outline in the tissue the desired shape of the patch, and tear along the line made by the needle. The shape can be outlined by either dragging the needle firmly along the tissue or by making a series of dots to perforate the tissue. You can also cut a slightly smaller piece of tissue to just fit the hole as an insert. This insert piece will make the repair look more opaque. The insert is sandwiched between the two oversize pieces of tissue.
To apply the lacunae repair: Place the damaged item on a piece of release paper; position one piece of oversize tissue over the hole. The tissue should slightly overlap all edges of the hole. Place another piece of release paper over the tissue and tack into place around the edge of the loss. Turn the item over and place the smaller tissue on the loss; tack into place. Tack the third piece of tissue into position just slightly overlapping the edges of the loss again. The mend is held to the item only at the edges and it is possible to see the three separate layers. Seal the three layers together by ironing over the entire area. Be sure to use the release paper. Let the mend cool for a minute under a weight. If the tissue repair overhangs the edge of the item, cut off the edges of the mend so that they line up with the edges of the item.
When possible, use the tissue on the back side of a paper. If the mend requires a patch on both sides of the paper, make sure the patches are NOT exactly the same size. The reason for this is that two thicknesses of tissue of the same size and position will form a point of stress or “breaking edge” and may be the source of another tear at that point. Heat set tissue is particularly successful when used on coated stock (slick, shiny) and on paper so fragile and discolored that it will not hold up to being wet locally.
If you want to match the color of the paper to be mended, use water color on the untreated side of the tissue but use a slightly LIGHTER color. After the tissue has dried, the heat used to apply the tissue will darken it.
Remember, this type of repair should not be done on archival materials without first consulting a conservator. Since heat set tissue can be removed only with solvent, and heat may damage some items, one must proceed with caution.