Preservation Practices

Transcription

1 Preservation Practices Improved Climate-Resistant Packaging by Hugh Phibbs Being able to provide a micro-climate package that can keep framed items safe from outside problems is vital to a well-trained preservation framer. To succeed in today's technical economy, your skills and knowledge must constantly be improved. Techniques and materials that may have been sufficient in the past must continuously be compared with other choices to find the best method. This is especially true for preservation framing, where there have been remarkable changes and innovations in the 25 years. Today we have hinges that do not deform even delicate papers, edge support strips that hold all sorts of paper items steadily and gently, and glazing materials that filter out harmful wavelengths of light and also have no static at all. There are also sequestering packaging materials and designs that can protect contents from wetting, extremes and fluctuation of humidity, molds and mildews, and a host of insects. Readers who have followed this column have seen an evolution in each of these areas. In the area of climate-resistant packages, the earliest example described employed plastic/aluminum laminate and double-sided pressure-sensitive tape. While this performed well, time and testing showed that it could leak microscopically where two pieces of tape crossed. This package could not be tested with pressure since that would blow out the pressure-sensitive tape bond. A subsequent design that used electrical grade hot melt glue for the tape could solve the micro leakage issue and stand up to pressure testing. But hot melt is messy and brittle, so it could crack and fail if its bond is stressed. A third adhesive choice, high tack 3M ATG 969, can solve the problems that affected the other adhesives. It fills gaps and does not have the problem of micro leaks where tape layers cross. The powerful hold of this adhesive and its lack of a carrier mean that it must be applied with great care. But even in thin strips, it can provide a pressure-resistant bond that will not crack if flexed. This material requires one important change: the sealing foil must be turned so that its heat bonding side is out and its puncture-resistant side is in, since the ATG will stick much more firmly to the puncture-resistant side. The addition of strips of ATG to close the corners of a package is the only other modification needed for successfully sealing matted materials using foil laminate and this adhesive. How can you use this to make a package that will hold for three-dimensional items? The package for a work in a mat can be sealed with heat applied to its edges, since the art is generally far enough away so that it won't be heated. This lets you make a package from one sheet of sealing foil. It would extend across the back of the mat 82 PFM _ November 2006

2 package then up around its sides and onto the outside edges of the glazing, where the foil would be bonded to the glazing. A painting does not have space around its edges that can allow for the safe application of heat. A painting or thick object package must be loaded from the back. For this, a package can be made of four walls that are bonded to the glazing along one edge and flare out across the back of the frame, where they can be heat bonded with a back sheet of laminate material along their other long side (Figure 1). Previously, the walls would have been bonded to the edges of the glazing with electrical grade hot melt adhesive. This posed two seri- Figure 1 ous problems. The adhesive was difficult to apply neatly to the glazing edge, and once the wall material was bonded to it the hot melt could crack or peel off the glazing. For those reasons, such packages required experience in the technique as well as in using frames with wide lips or rabbets. Since the 969 ATG can be used to make packages for matted materials, could it also be adapted to use with a painting or thick objects? The first obstacle is that ATG sticks to the puncture-resisting side of the foil and not the heat bonding side. For a matted item, you only need to turn the foil over and use the other side. For the painting package, however, the sides of the package should be made with two layers of laminate foil to provide the needed strength and rigidity. Since the walls have two layers, they can only be heat bonded to each other if at least one of them has its heat bonding side facing the other wall. A layer of the foil must be applied, punctureresistant side in, to the edges of the glazing so that the wall material can be heat bonded to it. Like packages, for works housed in window mats the 1 /4" tape is applied first to the edge of the glazing and then wrapped around and onto the front of the glazing sheet. With most glazing sheets, there should be slightly less than 1 /8" 84 PFM _ November 2006

3 Available from PFM P U B C O SECOND EDITION The Mounting and Laminating Handbook by Chris A. Paschke, CPF, GCF The second edition of this manual includes 16 additional pages, including information about various digital technologies. Designed as a technical reference book geared to both beginners and seasoned veterans alike, it is a complete source for basic techniques, hands-on procedures, applications, and tips. Topics include heat mounting, cold mounting, laminating, and creative mounting and laminating techniques. Softcover, 176 pages Item No. B543 $19.95 Name Company Street City and State Zip Phone Signature Check Visa/MasterCard Card Number: Exp. Date: Price $19.95 Quantity Order Subtotal +$4 shipping per book Order Total Make checks payable to: PFM PubCo., 207 Commercial Court Morganville, NJ of tape on the sides and a little more than 1 /8" on the front edges of the sheet. This allows the foil laminate to be adhered to the sides and the front of the glazing. This two-part attachment is important in holding the laminate tight to the glazing. A thin strip of foil laminate can be cut and adhered to the ATG layer with the heat bonding side of the foil Figure 3 on the outside. This first strip can be roughly 3 /8" wide. When it is applied, it can run around the corners of the glazing sheet so that its ends meet on one of Figure 4 the sides of the sheet (Figure 2). Next, eight strips of laminate foil are cut. Four outer strips are 3" to 4" wide and are longer than the side to which they will be secured by twice their width. The four inside Figure 5 pieces, which will reinforce the side walls of the package, should be 1 1 /2" to 2" wide and only as long as the edge to which they are attached. The outer wall strips can then be heat bonded to the strip that has been bonded to Figure 2 the edges of the glazing (Figure 3). Care should be taken that these strips are heat bonded to both the front and side of the first layer of foil. When all four sides have been bonded, the ends of the strips that exceed the length of the glazing can be pulled together so their heat bonding sides face each other. The heat applied to their outer surfaces will bond their inner surfaces, forming the beginnings of the corners (Figure 4). With the outer walls secured, the inner walls can be applied. First, a piece of matboard as thick as the glazing is laid under the foil laminate edges and against the sides of the glazing to keep the inside of the laminate coplanar with the glazing surface (Figure 5). A strong bond can now be started for the inner wall. This is done by laying down another strip of ATG that goes no 86 PFM _ November 2006

4 farther onto the glazing than the edges of outer wall did and which crosses onto the outer wall. The inner wall can be laid down with its heat bonding side touching the ATG, and then heat bonded to the inside of the glazing and to the inside of the outer wall (Figure 6). The fact that the heat bonding side of this strip will touch the ATG means that this bond is not as strong as it would be had the other side of the strip been stuck to the ATG. But the excellent hold of the outer wall to the glazing edge also Figure 6 Figure 7 means that this bond doesn't need to be very strong for the package to function well. With the sides secured, the package can then be stood up on one edge and heat applied to the corners next to that side to bond them along a line perpendicular to the plane of the inner surface of the glazing (Figure 7). The finished package can be fitted into a frame and checked to make sure that none of the foil laminate can be seen from the front of the frame. If any of the silver foil shows, it should be carefully trimmed with a blade and the excess material removed. With the package in place, the outermost part of the sealing foil should also extend across the back of the frame, forming a surface to which a sheet of foil can eventually be heat bonded to close the package. A spacer can now be added to the inside of the glazing to keep the painting away from its surface. Volara, a radiation cross-linked polyethylene foam, is ideal. This soft black foam material with a smooth surface can be found at preservation suppliers. After that, the glazing is given a final cleaning and the painting installed. A single sheet of the sealing foil is then laid across the back of the frame and bonded to the back of the package walls with heat. Once the package is closed, it can be secured in the frame with mending plates that are screwed into the frame and press against the back of the painting's stretcher through the foil. A final backing of polypropylene fluted board can then be screwed onto the frame to protect 88 PFM _ November 2006

5 the package and its contents. The first significant advantage of this design is the tenacious grip of its walls to the edges of the glazing and the fact that the walls can be secured to the glazing with only a small amount of the foil showing. A second advantage is that this package can be used with far more frames without their being rabbeted out or without anything added to the lip of the frame to cover the foil. As a result, this sort of package can be a practical and important part of the offerings of the well-trained preservation framer. If used to protect valued materials from climates that are too wet or dry over extended periods, it must be made using laminated glass to enhance safety. Conversely, if freeze-dried materials are to be kept dry indefinitely, they will need a package that employs glass since, unlike acrylic, it is a functional vapor barrier that will keep the contents dry. Being able to provide a microclimate package that can keep framed items safe from climatic and biological problems is vital to the repertoire of a well-trained preservation framer. Just keep in mind that items to be packaged must be properly conditioned, such as 50 percent humidity at 70 F. But that's a topic for the future. Hugh Phibbs, Preservation Editor, is the coordinator of graphics conservation services in the Department of Exhibitions and Loans, Conservation Division, National Gallery of Art, Washington, D.C. He has taught workshops for the National Conference, the AIC, PPFA, conservation programs at Winterthur/ University of Delaware, and the Smithsonian Resident Associates Program. He also compiled the matting and framing section of The Book and Paper Group Outline. 90 PFM _ November 2006