Palimpsests ancient and modern
This is a kind of follow-up article to a previous article about pairs ancient and modern for security. That article discussed how pairs help with security in old physical documents and objects, and also in modern electronic ones.
This article goes into palimpsests and other ways of partially erasing things, for old physical things and more modern electronic things.
Wax tablets
The first medium we will think about is a wax tablet. The ones I have seen (modern replicas of Tudor ones) are like a chunky wooden picture frame about the size of a mobile phone. In the place of a picture there’s a slab of wax. Often they come as a pair hinged together, a bit like a book.
You use a stylus or other strong pointed stick-like thing to carve lines into the wax, to write or draw. You can think of a stylus as being like a pencil, and at the top of some styli instead of an eraser there’s a wide stick going across so that the stylus looks like a capital T. You can wipe the wide part across the wax to smooth it again, to erase the lines you had previously carved.
They have been around from before Roman times – the photo shows a modern replica used by the Ermine Street Guard.
The word palimpsest comes from Ancient Greek via Latin, and is formed from words related to scrape and again. Scraping the broad part of the stylus across the wax removes existing writing so that the tablet can be written on again. It can also refer to washing or scraping ink (and some of the hide) from the surface of a parchment so it can be written on again. The key thing is that erasure might not be completely successful, so that some of the old writing remains when you add new writing.
Writing on wax tablets means you are carving it. If you took a slice through the carved tablet and looked at it from the side, you would see valleys and hills, similar to how soil is piled up next to a ditch when it is dug. (If there were no hills, where would the wax go that had to be displaced to make the valleys? If you treated this wax as waste and threw it away completely, you would eventually carve away all the wax in the tablet.)
When you partially erase it, you partly flatten the hills and partly fill in the valleys. Adding new writing would mean adding full-height hills and full-depth valleys on top. This accumulation of the generations of hills and valleys makes me think of Fourier synthesis, where complex waves such as the sound waves for music are built up from simpler ones such as sine waves.
Parchments
An interesting example of parchment palimpsests is the Achimedes Palimpsest:
This is a digitally enhanced photo showing one generation of writing going horizontally and another generation going vertically on the same bit of parchment. The document is medieval and originally was seven treatises by Archimedes plus other works. However, these were partially erased to create a Byzantine prayerbook (which is how the document appears today). Two of the seven treatises have been found nowhere else than in this document, in their partially erased form.
Palimpsests mean you have two documents in one. Sometimes parchment has another way of having two documents in one, which is when there are holes in one page of a book that let you see part of the next page. These holes are sometimes decorated:
Pen and chalk on boards
This is a brief interlude between the very old and the much more modern. There’s no deep analysis or thought, just pointing out that writing on boards with chalk or dry erase pen can also lead to palimpsests, as seen in films about the importance of language:
Electronic documents – storage
We now come to electronic documents. This will be in two parts; the first will concentrate on how documents are stored e.g. on your laptop’s hard drive, and the second will be about displaying documents and images.
Before we get to palimpsests, we need to think a bit about how documents are stored in computers. When you store a document (a letter, an image, a video etc.) on a computer, you write the numbers that represent it to the computer’s storage such as its hard drive. A simple way to do this is to add the document to the first free bit of storage after all existing documents. This works well until documents need to change in some way – they need to either get smaller or bigger or be deleted completely.
If a document shrinks, then there’s now a gap between it and the next document. This gap isn’t at the end of all documents, so it’s going to waste. If you don’t deal with the waste, you will run out of space sooner than you need to. You could avoid that by shuffling all later documents along to fill the gap, but this will take such a long time and happen so often that it’s not feasible.
If a document is deleted, then there’s an even bigger gap than if it shrinks, so the shuffling problem is even worse. If any document other than the last one wants to grow it can’t because the next document is in the way. You either have to delete the document from where it is and add it back after the end document (leaving a hole where it used to be as if it had been completed deleted) or shuffle all later documents along to give it room. In general, there’s a lot of shuffling with this approach.
One way of making this problem better is to divide the storage into chunks, often called blocks or pages. Instead of viewing the storage as one continuous thing like the enormous rolls of paper used to print newspapers, it’s now a ring binder full of separate sheets of paper. The size of the blocks can vary – on the Windows laptop I’m using to write this the blocks are 512 bytes big.
Actually, it’s best to think of storage as two ring binders of sheets of paper, which I’ll call binders A and B. To start with binder A has all the sheets and binder B has none. When you want to add a document to storage, you go to binder A, remove the top sheet, put it in binder B and start writing on it. If the document is too long to fit onto one sheet, you take another sheet from binder A, put it in binder B at the end, and keep writing. You repeat this until you’ve written the whole document.
When you want to add a second document, you repeat this process – take a fresh sheet from binder A, add it to binder B at the end and start writing on it. (Binder B has an index that lets you see where each document starts.) If you want to add a lot to the first document after you’ve added the second, you can just insert fresh sheets into binder B between the end of the first document and the end of the second.
This might be so straightforward as to be boring, but the interesting part is when we delete some or all of a document. When a sheet with writing on isn’t needed any more, it’s removed from binder B and put back into binder A so it’s available to be re-used for other documents. (There’s a detail that I’ve skipped over so far – if a sheet is taken from binder A and it has writing on from a previous document, this writing is completely erased.)
We can now get to palimpsests. Imagine I have a very important document on my computer that takes up 50 blocks (remember, these are the sheets in the binders). I accidentally delete the document, so all its blocks are put back into binder A. (Binder A refers to something in the computer called the free list, which lists all the blocks that are free to be used for new writing.)
The important thing to realise is that when you delete a document on a computer it isn’t erased – its storage blocks are made available for fresh writing, but the blocks still hold the information they had before I deleted the document. If I have the appropriate tools, I can reach into binder A, extract the blocks for the deleted document without erasing them, and reinstate the document. The icon you drag documents to is (on a Windows machine at least) called the Recycle Bin rather than e.g. Waste Disposal for a reason.
I might be unlucky when I try to undelete my document. It might be that since I deleted it I created lots of new documents, so some of the blocks that used to hold my important document have been used for a new document. So, my important document has been partially erased and replaced with other documents, i.e. a palimpsest.
There’s an important difference between a digital palimpsest caused by recycling storage blocks and a physical palimpsest in wax tablets or parchment. If you divide a wax tablet up into little squares, each square will have the current document plus a partially erased version of the previous document. If you look at the blocks that make up a digital palimpsest, a given block will be fully the previous document or fully the current document, but only some of the blocks will have been changed from the previous document to the current one. Digital palimpsests from re-using storage blocks are like a wall where new posters have been partially torn off to reveal old ones.
Old ripped poster on wall. Free public domain CC0 photo.
More:
View public domain image source here
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We’ll now come to a different kind of electronic palimpsest, where we can see all of both documents at once (like the physical palimpsests, and unlike the electronic palimpsests described above). This kind of palimpsest raises an interesting question, which is: What is a document?
If you look at this screen from an airport closely you might be able to see more than one document at once:
The current document is two columns, each column showing an airline and a number. There is also a trace of one or more previous documents. This shows up as a block of text at the bottom with a dark background, plus some text in and around the columns of text of the current document. This is caused by something called burn-in.
If a screen such as the plasma screen in the photo displays the same image continuously for a long time, it gets slightly damaged by the image. (You can think of it as it has worn out more quickly than normal, just in the spots where it was displaying the image.) Even when the screen tries to display another image, the damage means it’s still also displaying the previous image.
It’s important to realise that the two or more sets of storage blocks behind the images are fine. There are no partly recycled storage blocks as in the previous section. It’s just when the content of these blocks is displayed that there is blending. This takes us to the question I raised at the start of this section: What is a document?
There are two main answers I can see to this. The first is to do with the experience of reading and seeing the shapes of the letters and punctuation. With this answer, the documents are being blended. It suggests that the numbers in storage that represent the document are no more than a potential version of the document, and it doesn’t fully become a document until it’s turned into shapes that can be seen.
The second answer is that the numbers are the document, and the burned-in monitor is just something that helps you to read it, like a light that helps you read a physical book. The fact that someone can’t make sense of the numbers doesn’t stop it from being a document as far as someone else is concerned. Because I’ve been around computers for long enough, I know that the number 65 means the letter A if you use ASCII to turn letters into numbers, 32 means a space and so on. The image below shows a document, but because it’s in Akkadian I can’t understand it, although I know someone who probably can.
People and Metaphors
Palimpsests could be due to something as innocent as the efficient use of resources. However, they could be an exercise of power, if the original document was from one person, and someone else is trying to blot out the document (and maybe its author) with a newer one.
Some people are erased from history, and others aren’t recorded in the first place. Whose words are recorded, and who has control over their own words, are both very important.