I’ve asked a few art-producing friends if they’ve ever used vellum. They usually answer no, but sometimes, they say they have. After a few more questions it transpires that what they really mean is they’ve used paper that calls itself vellum. This is rather like asking a vegan if they eat meat, and they respond ‘yes’, only for ‘yes’ to mean they eat TVP and Beyond Burgers. If you google ‘vellum’, what you find is a bunch of paper products that outnumber hits for the real thing. Vellum is not a kind of paper!
Vellum is the heavily processed skins of calfs, i.e. young cows. Other skins are available, and they come under the (flesh-based) umbrella term ‘parchment’. You can have goat parchment, or sheep parchment. Vellum is the higher status product, and even higher status is ‘abortive vellum’. This comes from aborted calf foetuses, and is presumably very fine-grained and soft. As far as I’m aware, the latter isn’t commercially available anywhere. Allegedly, it was used in portrait miniatures in the 16th and 17th century, though I suspect normal vellum was used much of the time.
Vellum isn’t, err, very vegetarian. As I may have mentioned, it’s made of flesh. This lends vellum utterly different handling and storage properties to paper. Paper is basically a cellulose material, which means it is a naturally occurring polymer of glucose. Culinarily speaking, paper is a carbohydrate (though it has no nutritional value), while vellum is a protein (again, don’t actually eat it). Vellum does not burn readily (it is slightly fire-resistant), and would be very smelly if you tried. It does not get readily saturated by water, and has a naturally oily, greasy quality. It has a ‘flex’, an elasticity.

Why do all these pesky paper merchants get away with calling things ‘vellum’ and even ‘parchment’ that are nothing of the sort? Vegan meat substitute makers don’t call their products ‘beef steak’ or ‘pork mince’. No, they use euphemisms like ‘meaty strips’ or, at most delete vowels from real meat terms (chick’n; p’rk ch’ps; foi’gr’s).1
The reason behind this, of course, is that real vellum is so incredibly niche that there simply isn’t enough of a lobby or litigious force to protect the meaning of the term. In England, there is one maker of vellum called William Cowley (geddit?). I suspect they don’t have the financial resources to take the paper manufacturers to court over their bovine-free writing surfaces.
The raw material from which vellum is made, animal skins, is not itself valuable. William Cowley, at any rate, source their skins from the meat trade: in this context, the skins are a by-product with no apparent value. This also means, to my mind, that the purchase of vellum doesn’t support the meat industry which makes it fairly ethically sound in my book.

Though it uses a ‘waste’ material, vellum is very expensive indeed. Why? Because making it is such a labour intensive process. The last time I checked their prices, the cost of a 60cm by 30cm piece of calf vellum from Cowley was £106.84 excluding VAT and delivery; a piece of goat skin vellum of the same size came in at £62.12, excluding VAT and delivery. Confirming this, vellum made in developing countries is far cheaper. An entire goat skin’s worth of parchment made in India, sold on Etsy, is currently going for £30.65 (I can’t speak to its quality, and apparently it needs sanding down, to be fair!).
One day, many centuries ago, there wasn’t an alternative to this strange, labour intensive writing surface. Trade routes that took papyrus to Europe were gone, and so the only option was to flay an animal, bathe its skin in salt and lime, and scrape it for hours on end. Yet this product was not a terrible ‘prototype’ of paper: it is in many respects unmatched to this day. Unfortunately, for most of us, it is too expensive to use.
It is not at all clear that being a 'by-product' exempts vellum from all the ethical problems of the meat industry.
It's worth being being painfully literal and explicit that the meat one buys in the shop comes from an animal that, obviously, has already been killed. Choosing not to eat meat on a given occasion won't bring animals back to life; it is, primarily, a means to *cut demand* for products that are produced by torturing and killing animals. The argument is not that, if you choose not to eat a burger, the very cow you would have eaten will be saved - that cow is already dead before you decide on dinner. The argument is that on the margin, loss of revenue for companies that produce meat will cause them to produce less meat in the future.
By supplying a source of income that is (a) reasonably uncorrelated with demand for the primary product, viz., meat (specifically veal) and (b) does not come at the expense of their primary source of income, by-products play the role of a costless hedge for the meat industry, reducing their risk exposure and thereby allowing them to expand production more than they would without the existence of a market for by-products, and to experiment with lower prices for meat that can bring in more customers. How big is this effect? I'm not sure, I've not seen a good quantitative estimate; but it's certainly not zero, not when you take into account the sheer diversity of 'by-products' the meat industry sells. When the demand for by-products falls, you get farmers and slaughterers actively complaining about how it puts financial pressure on them (see https://www.foodunfolded.com/article/are-edible-animal-by-products-being-wasted), which they wouldn't bother doing if the benefit from selling by-products was negligible.
You can also see this another way, via the point that the category 'by-product' is vague at best. OK, vellum is a by-product with 'no apparent value' to the slaughterer. But then, are not yoghurt and buttermilk by-products of dairy production? Hell, is not veal itself often a by-product of dairy production? You are essentially relying on a distinction between products that the industry _intends_ to produce, and products it merely _foresees_ the production of as a side-effect of intentional actions; a slippery metaphysical distinction that collapses under scrutiny and can't bear the weight of thinking about the impact of our actions in a globalised economy.
Sure, when you buy vellum, the death of the calf is already 'baked in', and there's nothing you can do to reverse it; in that sense it is a mere 'by-product'. But that's no different from buying a cut of veal. In both cases, the relevant question is one of demand: in econ jargon, how much is the demand curve for shifted right by your purchasing habits?; how much are your actions enabling meat industry practices, on the margin? Buying £X of vellum almost certainly contributes to the slaughter of fewer infant cattle than buying £X of veal, but the number is not zero. And, more generally, a willingness to purchase _all_ 'by-products' without any ethical worries means that the relevant contribution comes not just from vellum, but from all sorts of other 'by-products' too, whose contribution has to also be added in. Altogether it is not an ethically neutral picture.