Home Blog Blog WSW Toolkit Foreign Correspondent–Animal Adhesives

Foreign Correspondent–Animal Adhesives

adhesives

Adhesives, part 1.
This one’s not just for the bookbinders! I recommend starting with this bit on what makes something archival for a little background. When I began trying to lay out something simple about adhesives per a request we had from a printmaking class (ages ago, they’ve probably figured it all out by now), I realized just how much is involved. What follows is, I hope, a simplification of a huge amount of information, but something that might help you choose the right adhesive for your project.

A little vocabulary: traditional adhesives are either vegetable-based (pastes) or animal-based (glues). Synthetics eventually replaced the animal adhesives in many applications sometime in the 20th century, so those are called glues too. And bookbinders, you’ll want to pay close attention to whether an operation calls for paste or glue or a mixture thereof (and hope the author was paying attention to that too). “Paste out the board” means something very different than “glue out the board” when all parties agree to that distinction. The family tree above gives you a vague classification of the adhesives—methyl cellulose being the outlier as a vegetable-based adhesive but a relatively modern one compared to wheat and other pastes. More on that later.

In the conservation (and industry) literature, tape is often referred to as pressure-sensitive adhesive, which referrs to the idea of applying it by pressing it onto a surface rather than, as in the case of liquid glue, brushing. Tape consists of one of the above kinds of adhesive plus a carrier–-the plastic or paper part.

Animal Glue small

Beads of animal glue

Down to business: animal glue. Here we’re talking about bone glue, hide glue, and gelatin, as well as some you might not have thought about: fish glues (isinglass), rabbit skin glue, egg white (albumin), milk (casein), etc. In your basic animal glue, the collagen (proteins) in the skins and bones of horses is extracted through a cooking and liming process, resulting in a transparent brown liquid when hot, and solid (pellets, usually) at room temperature. Gelatin is a more refined version of the same thing, closer to clear when liquid. You might have heard of egg whites, another protein, being used in tempera or other paints as the binder, or for gold tooling as a (weak) adhesive. Rabbit skin glue, processed in the same way as horse hide, has been a traditional adhesive for instrument making and sizing canvases. Isinglass is made by soaking the swim bladder of an appropriate fish (often sturgeon) in water, then heating it to release the proteins, and straining the solids away. Casein is one of the components of milk; to turn it into an adhesive the milk is curdled, and the curds treated with an acid to precipitate the casein, which is then purified and dried. It’s been used as a size in papermaking, as a stiffener of textiles, and as the binder in paints for a long time.

Gelatin (powdered)

Gelatin (powdered)

Protein is complex enough to keep the chemists occupied for a while, but for our purposes what’s interesting is that it can be super sticky. These glues make strong but brittle bonds: look at a falling-apart old case-bound book and you’re sure to see the yellow-brown animal glue on the spine cracking apart from itself and the paper. As conservators we like the stuff, compared to synthetic glues, when we need to remove it, because it swells (gets soft) easily in water. It is possible for some of these protein adhesives, particularly casein, to cross-link (form more and more chemical bonds to itself over time) and thus be less responsive to water or other attempts to soften and remove it. When would we use it? The more purified gelatin or isinglass would usually be used instead of generic animal glue in conservation, although bookbinders still slap bone and hide glue all over the place, and we’d choose to use it where we need a water-reversible adhesive (i.e. not PVA) that’s stronger than paste (also water-reversible). Examples might be where a particularly stiff spine is required, or in the repair of parchment, or, diluted a bit more, to re-adhere pigments flaking off an old manuscript.

Comments

  1. wrote on January 13th, 2012 at 5:04 pm

    Brahma Barry Johnson

    Thank you very much for shedding light upon such a sticky theme. My wife and I have been vegans for 39 years, yet still need to find ways of eliminating the use of certain products which are normal in households, yet contain animal based substances.

    The avoidance of anything derived from animal in food and drink intake is the relatively easy part. Not that much harder, but needing longer to implement, is the elimination of animal elements in clothing. Finding cosmetic and cleaning products which are totally animal-free is an ongoing challenge.

    Animal hair in brushes, feathers in duvets, all have non-animal alternatives – but adhesives are SO widely used – and how can one know which kind has been used. We love books – have many – what can we do about that? We were both career artists, yet art materials in general have so many uses of animal-derived components in their make-up. Okay, yes synthetic brushes are good replacements, and we use them, yet paper coatings, the adhesive used in pad spines, books, photo paper gloss – all such common things are so difficult to avoid, because in most cases, finding out whether an adhesive is animal, vegetable or chemical-synthetic based seems so hard. This blog is certainly a useful set of pointers, and we are very grateful for it, yet any further information you may be able to provide, to point out just where animal or non-animal adhesives and coatings are used would be much appreciated by my wife Sarasvati and myself.

    Sincerely,
    Brahma Barry Johnson

  2. wrote on January 28th, 2012 at 2:13 pm

    Abigail Uhteg

    That’s a tricky one! With new books you’re probably safe; it’ll be cheaper now to use synthetic materials for most manufacturers. I have seen recently-published books coming from India bound with animal glue on the spines, and don’t know what’s in your library, but if you look down the back of western books, at least, you’ll almost certainly see the white or pale-yellow hot-melt adhesive that’s much more common (often quite a lot thicker than it needs to be!). Same for the adhesive on tear-off pads.

    Sizing must be the most difficult one because you can’t really see what’s on the paper. Blotting paper and anything else made to be super absorbant won’t have any size at all. Newsprint will have less than book/printer paper, and at this lower end paper will tend to be internally sized (i.e. the size is in the vat at the time the paper is made), while very high quality paper is more likely to be surface sized (size applied after the sheet is formed). And from what I know—although I really know very little about modern machine-made paper—internal sizing is organic chemicals, maybe natural materials like rosin, but not animal-based. Surface sizing may be gelatin only, in the case of nicer handmade or mould-made papers, or gelatin in combination with other chemicals in more mass-produced papers. So maybe you’d have to do some digging on really nice resumé paper or stationery but probably that copy of Harry Potter is compatible with your goals. Unfortunately, as I’m sure you’ve found out, manufacturers might be reluctant to give up proprietary information such as what specifically they’re using but maybe they can tell you whether or not it’s animal.

    Historically, gelatin was used as a size in the west between about the end of the 13th c. until the 19th—for more on early paper, see this excellent site: http://paper.lib.uiowa.edu/european.php In the east, and before that in the west, paper was sized with starch.

    If anyone else has better information, please weigh in!

Add a comment