For the past 20-plus years, as long as I have been in the library marketplace, customers have been asking me for an inexpensive, easy to apply label that really sticks to books and last forever, yet is easily removable and never damages the book. Such a label doesn't exist, and the very basis of the question results in a moving target. Library vendors have developed several different formats over the years, each addressing important components of the question. The following is a brief description of label formats easily obtainable from the various vendor catalogs. Your own circumstances will dictate which is best for you.
Popularly known as the SeLin label process, these labels are the most permanent yet easily removable labels for cloth cover books in the market today. Several library vendors make these labels using different technology. They are a "plastic-like" thin white material, coated with a heat sensitive dry adhesive. These adhesives are not technically "archival" quality. They actually melt into the nooks and crannies of the cloth coverings and permanently bond to the material. To reverse the process, you simply re-heat the label, liquefying the adhesive, and remove. Most use two components, a base material with a clear overlay applied after the printing process. You use either a dedicated typewriter with a laminating device or a new automated electronic laminator linked to a standard dot matrix printer.
Although still the most permanent labels available today, the technical processing function is quite lengthy and expensive. Most users are academic or large reference li-braries. Vendors are in the process of developing new, easier to use SeLin label products.
These labels are a sandwich of paper, laminated to foil which is coated on the back with a cold application pressure sensitive adhesive. Developed especially to conform to the rounded shape of a book spine, these labels have a "memory" that lets them retain the shape of the curved spine. This memory feature helps prevent the label from "picking" up in the corners. Although pliable, the foil center produces a strong inner core that creates a barrier, preventing the adhesive from migrating to the front surface and discoloring the white surface paper. As an additional benefit, the barrier foil core prevents the adhesive from bleeding thru to the surface and causing the printing inks to fade. The foil core's opaque surface also makes it an excellent choice for use over existing labels.
Not all foil-back labels are alike as the quality of the adhesive is a vital component in long term adhesion, especially to buckram book coverings. Some are manufactured from a standard foil-back material originally developed for pharmacy bottle labeling. Several library supply manufacturers have developed their own material, obtaining smudge-resistant white acid-free paper, laminating it to a layer of foil and coating it with a cold application adhesive especially formulated for the various book coverings of today. Some library supply companies will provide long term aging and adhesion test results from independent laboratories.
A foil-back label with the proper library-specific adhesive is the best cold application label available. It's also the most popular form of spine label used in libraries today. It usually forms a permanent bond with all paper and box board materials and adheres well to most book cloths. It's available in sheets, rolls and pin-feed formats.
Please note that foil-back paper stock does not work in most laser printer applications.
Paper labels consist of a layer of paper coated with a cold application adhesive. Most adhere well to porous paper or box surfaces if the label has a permanent adhesive coating. They are good, all purpose economical labels but usually do not adhere well over the long term to cloth book coverings, hard surface box board or plastics. The adhesives can bleed thru and discolor the label over time and attack the printed message.
The varieties in the market are almost endless. The best were ones developed specifically for the library market. Several vendors purchase smudge-resistant, acid-free paper and coat it with their own library-specific adhesive formulation. These labels work extremely well on paper surfaces such as book jackets or the endpapers in books. Some varieties also work well as bar code labels on the flat surface of front or back covers.
They are available in sheet, roll or pin-feed formats. Most work well in laser printers.
Prior to the invention of the foil-back label, fabric labels were popular. They are strong, resist tearing, last longer than paper labels and conform to the shape of the book spine. How well they adhere to cloth books is dependent on their adhesives. None have the specially formulated book cloth adhesive used on the foil-back label, described above.
They do not accept print well, as the cloth tends to break up the letters and the inks feather around the edges. They have become one of the most expensive alternatives as their popularity has rapidly declined in the last few years. They are available in sheets or roll formats.
Many libraries are covering their labels with a clear vinyl or polyester overlay. The primary function of this protector is to help the label stick to the book by covering it with another clear layer with a much greater adhesive surface area. The protectors are generally much larger than the label itself. Some libraries also use them to keep the original spine label clean and in pristine condition. Most bar code labels that are produced "in house" on a dot matrix printer require a label protector to help prevent scratching the code during scanning.
Library supply companies have developed several different formats, usually related to thicknesses (1.5 & 4 mil). The heavier version is generally easier to apply and adheres well. One vendor has added a UV inhibitor to help prevent fading of print on the label.
Specifications are available from some library supplier sources. They can tell you the pH of the face sheets, the material components of the label format and indicate if the adhesive is an acrylic polymer or copolymer. However, many times the adhesives are proprietary formulas, developed over a lengthy period of time.
The Library of Congress has developed their own specifications with recommended test methods. It isn't quite finished as of this writing but will most probably result in several of the library suppliers testing their own brands under similar conditions.
An ANSI committee under the leadership of Jennifer Banks (MIT) is presently working on standards for label specifications and testing. They are coordinating their efforts with the Library of Congress and will be using some of the LC data as the basis for their recommendations.
Of course, all pressure sensitive adhesives are quite sensitive to your own library's particular environmental conditions. Adverse heat & humid conditions cause adhesives to liquefy, bleed and lose their tack. Face papers as well as print quality will also be affected.
If you don't have access to some of the sophisticated testing recommended by the Library of Congress specifications, I would recommend the following simple procedure:
Purchase a package of labels from each of your favorite library suppliers (Brodart, Demco, Gaylord & Highsmith) or from a local source. Take several typical books and place a label from each vendor on the spine and front cover. Be certain to "burnish" each label with your finger to assure overall adhesion. Mark each label with the date & vendor. Be sure to select the type & size of label commonly used in your library. Place the books on a shelf in the library and leave them in place for three months.
Remove the books and try to peel each label. This will very quickly identify the best labels suitable for your own library environment. You may be quite surprised at the difference in adhesion. A good label will not "pick up" at the edges and cannot be removed without destroying itself.
Plastics are difficult to label as the adhesives cannot permanently bond to the hard surface. Foil back labels developed for library books seem to work best. The labels stick well initially and the foil creates a barrier, preventing the oily surface of the plastic from bleeding through and discoloring the paper label surface.
Many large libraries have developed their own special formats from local vendors, but there are too many to mention here. If someone you know has such a label, simply obtain a few samples from them and include it in your "do-it yourself" test procedure.
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