© 1991 Jack C.Thompson
When paper is made by hand, there is little or no grain direction; the paper will expand and contract more or less equally in all directions as the relative humidity (%RH) increases or decreases.
As a sheet of paper absorbs moisture it grows in size. Anything which restricts this growth will be reflected in ripples, known as cockling.
The method chosen for framing will also affect how serious the cockling may become. A print which hangs from paper hinges will cockle less as the humidity increases than the same print would cockle if it were taped all around the edges to the window mat or back mat. Prints which go right to the inner edges of the frame are more likely to cockle than prints which are at least an inch away from any inner edge of the frame; if the print is in a wooden frame, that inch of separation will also reduce the migration of acid from the wood and the environment to a very small value.
When the temperature of the air in a room increases, the relative humidity decreases. The reverse is true inside a picture frame; as the temperature increases, so to does the relative humidity. This is because the increased temperature drives object humidity out of the object (in this case, the art work and mats) and into the micro environment formed by the frame.
If the fluctuation in temperature is gradual, taking place over a period of hours, the potential for immediate damage is minimal; if the fluctuation is sudden (especially if the temperature rise is more than fifteen degrees) moisture may condense on the inner surface of the glazing.
This problem is most likely to occur when a framed piece is exposed to natural light. Incandescent light (because of the infra-red component) ranks next, with fluorescent light being least likely to cause temperature changes within a frame.
All light can cause fading or darkening of pigments (some fade and some become darker). Sunlight, because of the amount of energy it contains, causes the most rapid changes in the physical properties and optical characteristics of art. Fluorescent light, because of the amount of ultraviolet energy it transmits, ranks next to sunlight as a source of damage to art work. Incandescent light is the least harmful source of illumination, but it, too, causes some colors to fade.
It is for these reasons that it is recommended that light levels in galleries and other viewing areas be kept low. For art on paper, the level of illumination should be no more than 150 lux (1 lux = 10 ft. candles). If the source of illumination is natural light or fluorescent light, the art should be protected from ultraviolet energy through the use of UV filters; infra-red energy from incandescent light is not a significant concern if the light source is at some distance from the art and the level of illumination does not exceed 150 lux.
Paste & Paper
Wheat starch paste and water cut hinges made from Japanese paper will adequately support just about any imaginable work of art on paper, with minimal damage to the paper support. Commercially available adhesive tapes are often used by graphic artists and picture framers as hinges but all of them will cause problems in time, including those which are sold as "archival" tapes.
The recipe for wheat starch paste which I use is: one part starch to five parts water. The water and starch are stirred until there are no lumps and then cooked in a glass, enamel, or stainless steel double boiler until done. The paste will become quite thick before the cooking is complete; a good way to tell if it is done is to drop some into a container of water and see what happens. If it diffuses into the water it has not been cooked long enough; it should stay together as a translucent solid.
There are many kinds and grades of Japanese paper. It is less useful to memorize their names or fiber sources than it is to develop a sensitivity to an appropriate relationship between the paper used for an art work and the paper chosen for the hinges. The hinge paper should be strong enough to hold the art in place during normal display or movement, but weak enough to break without tearing a piece out of the art work if the frame should be dropped.
When Japanese paper is cut for making hinges, do not use scissors or a paper cutter as that will leave a hard, sharp edge which will eventually damage the art work. Instead, draw a line with water using a wide, thin brush or ruling pen; fold the paper at the (narrow) wet line and pull the paper apart. There will be a number of paper fibers showing at the edges of the paper, and these will do most of the holding when the time comes.
When the art is ready for hinging the paste should be strained through a fine mesh cloth, such as silk screen fabric, to remove any lumps and make the paste easier to work. If it seems too thick it may be thinned with a little bit of water, but it should not be made runny. A little paste is then rubbed out on a smooth flat surface (glass, formica counter top, etc.) until it is smooth and level. The paper for the hinge should be examined to see which is the rougher or duller side and that is the side which will take the paste. Make certain that the drawn-out fibers are not all balled up and draw the hinge down onto the paste. The fibers, and between 1/16th to 1/8th inch of the hinge paper, should be wetted out by the paste before the hinge is drawn away from the paste and applied to the back of the art work. With the hinge in position, lay a piece of waxed paper over it and rub it down lightly before placing a blotter and a weight on it.
Later, the other end of the hinge(s) may be attached to the back mat and the art is ready for a window mat, glass, stiffener (if required), frame and dust cover.
In the case of items which must be viewed from both sides, a double window mat is used, with the item sandwiched between the mats. Except for very small items (up to about 5" X 7") two 4-ply mats or one 6-ply mat should be used on each side.
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