 In one of America's busiest cities, men and women dedicate themselves to the preservation of the treasures of the past for the present and the future. In the restoration laboratory of the Brooklyn Museum in the city of New York, scientists preserve cherished paintings from all over the world. We see the treatment of an 18th century European portrait under the restorer's hand. In the course of restoration, nothing is taken for granted, and every fact about a painting is proved as much as possible by scientific procedure. The portrait is an oil on canvas, signed and dated presumably by the artist. For modern laboratory examination, a painting must be removed from its frame. Old nails besides telling us that many years have passed since restoration was last done may provide clues to the painting's history. In the back of the canvas, too, discloses much about the painting, who has owned it, where it has been shown, and may even reveal previous restoration treatments. In modern restoration procedure, photographs are taken to record the condition of the painting before restoration, since no restorer can tell in advance exactly what will be discovered once treatment is begun. Because in any scientific operation, detailed records are kept throughout the work. Sometimes the restorer discovers that a painting has been backed by a second layer. When paint is cracked and chipped, a new lining is usually called for. Examination of the fluorescence of the painting's varnish coating under ultraviolet rays may disclose old retouchings of damaged area, a weak spot that necessitated lining in the past. Microscopic examination of the canvas provides information that may establish more definitely the extent of the damage, and magnification of particles of pigment can help place the approximate date of a painting, since pigments which are common today were unknown a century or two ago. As painstaking as the examination is the preparation of the painting for scientific restoration. Before restoration is begun, the face of the painting must be protected. Thin, strong mulberry tissue is attached to the painting surface with water-soluble paste and seals loose flakes of paint in place. As in most scientific procedures, materials and techniques from all over the world contribute to the job at hand. Mulberry paper comes from Japan. Paper can be used instead of the tissue, and in the United States, new wet strength papers are being developed. Allowed to dry, the mulberry tissue holds the face of the painting immobile. No matter how fragile, the painting, however, must be loosened from its old stretcher before treatment can continue. There are various methods to hold and support a painting during restoration. A paper work frame was devised by the Dutch in the 19th century. As early as 1857, it was employed in treating Rembrandt's famous painting, The Night Watch. In the Dutch method, with the oval painting still resting on its stretcher, its outline is drawn and cut out of ordinary brown paper. For paintings of the usual rectangular shape, straight-wide strips of brown paper may be used. The temporary stretcher is accurately squared off around the canvas. For great care must be taken to keep both painting and temporary stretcher on the level surface to avoid uneven stress on the painting as restoration continues. A heavy starch paste is used to soak the paper spandrels and fix them to their temporary frame. Paste is one of the few materials now used in restoration procedures that contains water, since water mixtures tend to promote decay and rotting of the canvas. When secured to the painting edge and work frame, the paper spandrel form a bridge. Constant cleanliness is necessary in the restorer's craft for any particle of foreign matter on the work table mited here to the painted surface. For an eight-hour period, the paper frame dries tight and strong, holding the painting as securely as a surgeon's c-clamp. It has been said that restoration requires the patience of a jolt, but the skilled restorer knows that nothing can be hurried in his work, for success depends on exact control of each step. An ordinary household vacuum cleaness serves its purpose in the restoration laboratory. Sometimes the restorer discovers the painting backed by a lining canvas. Such a backing indicates that the painting has been weakened and restored in the past. Most paintings over a hundred years old have undergone re-lining at least once, for a canvas is just a web of linen threads, easily damaged by rapid changes in temperature or accidental knocks and blows. The old adhesive must be scraped off with great care for the surface of the painting lies just beneath it. A study of the dried-out adhesive helps date the painting. The glue-paste particles indicate that the work was probably done in France about a century ago. The painting must be strengthened now by a strong new lining and adhesive. To give body to the old canvas, a wax mixture is prepared. One formula used in the Brooklyn Museum Laboratory is made of microcrystalline wax, Canada balsam, damar resin, and beeswax carefully weighed and melted. Until about a hundred years ago, glue-paste mixtures were generally used. But taking his lesson from Roman wax painting still chemically unchanged from ancient times, the modern restorer prefers chemically stable, moisture-resistant wax-resin formulas. A heavy coat of wax-resin mixture is applied to the back of the canvas to give it new firmness. Melted, it soaks into the canvas. The iron is just warm enough to press rayon about 150 degrees Fahrenheit and cannot scorch the delicate painted surface. Wax penetrates now to the front and seals in loose inflakes of paint. The wax-resistant facing paper keeps the painting from sticking to the work table during ironing. An old painting must be backed by a strong new lining. The new lining is carefully selected. For any unevenness in the lining fabric would be imparted to the surface of the painting. Various painting surfaces have been used by artists over the years. While metal or glass withstand age relatively well, canvas and wood gradually decay, and sooner or later must be strengthened. For a painting on canvas, a lining of strong unbleached linen is usually preferred. Modern restorers frequently treat the backs of paintings on canvas and wood with mold-resistant chemicals. And the temperature of modern museum galleries is carefully controlled to protect works of art from excessive heat and dampness. Stretched, shrunk with water and restretched, the linen lining is prepared with proper tension and firmness, like an artist's canvas. Experienced teachers the restorer just how much adhesive to use and how much pressure to apply. The surfaces of some paintings are relatively smooth, but in others, such as those by Van Gogh, the artist's brush has piled up pigment and textured masses, and too much pressure from the restorer's iron would damage the surface. And now, with the new lining attached, the Dutch work frame of paper is no longer necessary. Constant concern for detail assures that every step will fit the one preceding it and is planned for the one that follows. And now at last, the restorer can enjoy the satisfaction of working on the face of the painting. The gentle water sponging dissolves and washes away the facing tissue of mulberry paper. Stubborn spots of paper are removed with a scraper, and the rinse of petroleum benzene cleans away superficial wax and surface grime. Now at last, the dark film of varnish that has hidden the artist's crude tones and colors for many years may be cleaned away. The original paint beneath the varnish is most meticulously protected during the cleaning with solvent. Many chemicals are available to the modern restorer for the removal of old discolored varnish. His choice depends on knowledge of the artist's technique and the pigments used. A few test areas are cleaned first to determine the best solvent or combination of solvents for the painting in question. Having selected a mild mixture of acetone petroleum spirit and diacetone alcohol, the restorer cleans the small area at a time slowly and thoroughly. Often solvents of different types are used in different areas of the same painting. For chemicals that would not harm a solidly painted area of lead white, might remove a delicate glaze of Prussian blue. Now at last, the signature and date are clearly visible. Adolf Wirtmüller, Paris, 1784. Each step of the restoration has contributed evidence that supports the credibility of the date and signature found on the face of the painting. In keeping with the searching approach of lute, the 20th century restorer strives to preserve only the original paint and to remove all later additions and changes. Sometimes, solvent alone will not dissolve stubborn fly specs and a tiny surgeon's scalpel may be needed to help remove them. Ultraviolet rays reveal that old varnish still remains on the background although such areas are invisible to the eye. At last, old paper edging, from previous restorations is carefully scraped away. Again and again, concern for detail is seen to be vital to the success of the whole. Since cleaning may have weakened the grip of the new adhesives, another ironing, followed by pressure, applied with an ordinary glass tumbler, helps to complete the bond between the painting and its new lining. Just as an architect knows that a building is no better than a building just as an architect knows that a building is no better than its foundation, so the modern restorer knows that the foundation of a picture, its canvas, must be sound and strong. Wax on the surface easily removed with petroleum benzene shows that the adhesive mixture has thoroughly penetrated the canvas. So long as the old stretcher is strong, it is wiser to use it again as one's own clothes fit the wearer best, so the old stretcher best fits the form of the painting. The delicate curves of oval stretchers are difficult to duplicate today, and most stretches of this shape date from the days of hand craftsmen. Modern stretchers are generally mass produced and rectangular. Oval shape presents special problems, and exact cuts are required to fit the canvas smoothly around the curved edge. The restorer knows that mold and dampness can attack the sides as well as the back of a painting, if the lining canvas is not soaked with wax and ironed into place. The good restorer is as concerned about the appearance of the back of the picture as about the front, and in the tradition of the old-fashioned craftsmen, strives for the greatest possible neatness. Everything possible is done to ensure the soundness of the foundation of the painting. Little wedges of wood, called keys, dipped in the wax adhesive, expand the stretcher gently and tighten the canvas to its frame. A modern synthetic resin, polyvinyl acetate, is sprayed on the painting to isolate the original paint before retouching. The spray gun makes possible the application of a thin mist of varnish that dries almost immediately. Synthetic resins are used today because they are believed to yellow less quickly than natural ones. A white putty made of gesso, known since Egyptian time, makes areas where paint is lost and canvas damaged level with the rest of the painting. In the hands of the skillful restorer, the gesso fills in losses, but never covers original paint. Gesso-filled areas are absorbent and must be coated with a cellulose acetate solution before retouching. A photograph records the painting in its stripped-down condition to show what is left of the original paint with all retouching removed. Valuable information for scholars and appraisers. And now the restorer plays the role of painter, for colors must be mixed to conceal the gesso fillings and match the surrounding paint. In the past, oil colors were often used in retouching, but their tones yellowed with time and no longer match the original. Now, color ground in polyvinyl acetate or polybutyl methacrylate is used. Mediums of synthetic resin, which are believed to withstand age well. A final protective coat of polyvinyl acetate is applied and allowed to dry thoroughly. In modern restoration practice, nails are no longer acceptable in securing the painting in its frame for nothing should weaken the stretcher. Instead, gentle pressures from metal strips fixed only to the frame hold the painting in place and make it easily removable for future examination. A cardboard backing keeps out dust and protects the finished painting from accidental blows. Finally, the restored painting cleaned and protected to last for many years. With modern research to aid him and the free exchange of scientific ideas from all over the world, the restorer today can feel confident in preserving the world's works of art and making restoration a blend of science and art in the 20th century.