But leather, organic as it is, needs upkeep. And old leather books, especially if they've been in the sun for a long time or even if they've been treated well but are just very old, need the occasional reconditioning.
To show you that I mean business and have great faith in this technique, I'll demonstrate it on a book that is very dear to me: my copy of the Geddes Burns, one of only 473 facsimiles ever made of a specific copy of Burns' Poems, Chiefly in the Scottish Dialect in which the poet himself inscribed various clarifications, additions and brand new poems.
When it came to me, this book was dry as a bone. While most of the cover looked quite alright, the spine was dry as the Namib desert and had what looked like small spots of water damage.
the treatment: short versionMix up 3 parts lanolin and 2 parts boiled linseed oil, rub it on the leather with a soft cloth, buff it out with another soft cloth, leave it for 24 hours, then wipe off whatever's left and leave it to dry for another day or two. Repeat after at least a day if necessary.
After conferring with a few bookbinders (and one cobbler), the consensus seems to be that the desired mix of oils is this: three parts lanolin to two parts boiled linseed oil, measured by weight.
Lanolin, or wool grease, is the oil that comes off wool as it is spun. It's more or less the same grease that makes our hair greasy when we don't wash it. It's solid but malleable at room temperature, and crucially, it's stable across any temperature a book is likely to encounter, becoming liquid at about 40°C. Other potential but unsuitable oils would be coconut oil, which alas melts at 24°C, or beeswax, which melts around the same point as lanolin but is far too hard to use at room temperature.
Linseed oil, in this case, acts as a bit of a softener for our mixture, making it easier to rub on, but in the long run it has a fortifying function as linseed oil hardens over time. We don't want our leather to turn rock hard, of course, but the relatively small amount of linseed oil in the oil mixture makes sure that won't happen.
You can get lanolin at some supermarkets, but you'll probably have more luck at a good drug store. It'll sometimes go by other names, such as wool grease (or wolvet in Dutch). Not the cheapest thing in the world, but a little bit goes a long way.
Linseed oil you can get at most supermarkets or most any place that sells olive oil, sunflower oil and such. It's cheap and quite useful for a variety of things. I use it to oil up my tobacco pipes, for instance.
Wrap your pages, all held together as a stack, in your bog standard printer paper. Try to wrap up the block of paper as though you would wrap a present, making sure there are no parts of pages exposed to the air. It's especially important to cover the bits near the spine, as applying the oil there is quite finicky and you need all the help you can get.
I use printer paper for this - it's obviously not oil proof, but as it's only intended as an insurance policy and won't be smothered in oil, it's perfectly alright for our purposes. If you do get a big smudge of oil on your paper, carefully wipe it off before it soaks in and if it does leave a stain that looks as though it may bleed through, replace the paper before continuing. That last part is a pain in the old backside to do, so I recommend taking the next steps slowly and carefully.
Now, get some toilet paper - the softest you can get. We could use a towel, or some other soft cloth, but the nice thing about toilet paper is that it comes apart easily and that means that whenever it snags on some bit of leather or gold leaf ripple, the paper will tear rather than damage the book. You may end up with some bits of paper left on the leather, but those are easily wiped or picked off.
Fold up two or three squares of toilet paper into a little pad, about half the size of a playing card. Dip it in the wax, take a deep breath and start applying it to the leather. Go gently, don't press too hard, and take another dip in the wax rather than trying to spread small amounts too thin.
Now, you may notice an immediate darkening of the leather, or it may take a while, or it may just get shinier and not appreciably darker. It depends on the leather and the state it's in. One thing you may notice that may worry you is a splotchy appearance - that is to say, you'll see darker and lighter areas. While this can be inherent to the leather (whether it was poorly dyed in the first place, or damaged later), usually it's a temporary effect that disappears as the wax soaks into the leather and evens out, usually over the course of about five or ten minutes. So don't worry too much.
It's recommended to oil up the entire book in one go to prevent visible lines between old and new treatment, but if you cannot oil up the whole thing, make sure those 'seams', if they do show up, will show up at the book's natural seams. So oil up the front cover right up to the joint with the spine, leave it to dry, then oil up the spine, et cetera. But again, if you can manage it, oil up the whole thing.
Though this particular book isn't that old (as books go) at 113 years, the leather was quite dry. After applying a first treatment, the leather started to look dry after about an hour and I waxed it up a second time. It stayed shiny and has ever since.
After that, get the toilet paper back out and carefully, while touching the leather only with toilet paper or cotton gloves, buff the book to remove whatever oil remains on the surface. Wipe that bad boy down. Once you've got it looking good, that is to say well saturated but not 'wet', leave it for another day or two.
After that, you're done! It is said that if you really want to take good care of leather books, you should never touch them with your bare hands - but wise beyond our years as we are, we know that holding a leather book in one's bare hands is half the fun so we do it anyway. They're made to be handled, after all.