Carving in stone

I originally posted a version of this in the summer of 2016. I’m reposting it with some minor edits.

A classic way to make something permanent is to carve it in stone. So much so we hold it in our language with phrases like “It isn’t written in stone yet.” Using a chisel and hammer the shapes are able to survive many elements and human activities for centuries to millennia. For evidence of this all we have to do is look at our historic records. Those written in stone are more common as we go back in time. Paper can survive as long given proper care in the making and storage of the documents. Paper though requires heroic effort to make it into the centuries. Stone requires some effort to get rid of.

Stone survives a lot of weathering, touching, rubbing, vandalism and even some attacks. It is a generally low density storage media though. As you chisel bits out of the face you can only represent so much before running into problems. Shrink the chiseled marks and the feature’s finer details may not be as robust. At what point is the distance between features so small that normal wear takes its toll sooner? When do the features become so small that they can’t be kept clean enough to observe? Dust and dirt become the enemy over time in these cases.

Ignoring the choices of stone type (yes they vary wildly in resistance to scratching, pounding and the elements), we can define some basic features that make stone good and/or bad for preservation of information.

Information carrying

As I pointed out earlier, stone has a rather low data density, especially when we want the information to survive a long exposure to unknown elements. With a the ability to carve a fine point we can make marks in stone that are on the order of 100 Dots Per Inch (DPI), but the raised stone between them can be fragile. As the depth increases the likelihood of the feature breaking goes up. If the mark is shallow we run the risk of the feature filling up or wearing off early in the life of the carving. I haven’t been able to find any guidance to the survivability of carving features. Looking at older carved items I think we can use old screen resolutions with some care, so let’s start with 72 DPI.

At 72 DPI we can carve a rough page of text or represent low resolution B/W images. That is good for conveying a story for generations, but it won’t work for more generic data, or when we need to send a modest amount of exact values into the future. For that we need to digitally encode data. The first place my mind goes for this is to use the dots as bits.

Say a dot is a 1 and no dot is a 0. We will need some sort of guard band around each dot. That limits the number of dots to a 3x3 grid for each bit for a whopping 576 bits/square inch. You can have each dot share a guard, but any attempt to shrink the spacing will make errors a bigger problem. These can occur from a carving mistake, stone defects or physical damage. keeping the dots cleaned at that density is far from ideal and freezing water could cause damage over time.

2D barcodes are an easy way to increase the density and handle the resulting errors. Most of the barcodes, like the Datamatrix example above, contain some error correcting codes that can survive parts of the code being unreadable. Many of the 2D barcodes are tunable to the amount of error they can recover from using Reed-Solomon error correction. In some cases the information can survive most of the code’s destruction at the expense of data density. The edges form a type of spacing clock. A reader can tell roughly what the spacing is even if only a fraction survives and no guard bands are required in the data. Even with a high recovery setting the 2D barcode should still be more data dense than the carving of bits or letters.

The problem is how long in the future will any of these barcodes be decipherable? Would we need to surround them in pictures explaining how to decode them? Can that type of decoding even be expressed without some complex shared language and concepts? I hope to get into those details in future posts as it is at the heart of Anticryptography.

For now I think simple drawings and letters are the best bets for stone. Maybe leaving plenty of room around the writings, hoping someone carves translations in more modern languages over the millennia. The Rosette stone was a miracle for understanding ancient languages for that reason.

Survival

Given enough time, things will happen to any carrier of data. It is just a given from a probabilistic sense. What are these and what effect do they potentially have on our stone carvings?

• Water: Exposure to water is a given. Outside it might be exposed to rain. Even inside or under shelter condensation from humidity can collect. Running water can cut stone given time. Fast running water can drill holes and act like tools on a stone face. Water that fills a feature and freezes can expand and fracture stone.

• Dust/Dirt: When blown across a surface they can slowly erode features flat. When allowed to settle they can fill and cover features thus obscuring information.

• Heat: Changes in temperature can cause stone to crack. Fire is an obvious cause, but it can be more mundane. Continued exposure to sun and ice cycles may cause damage over years.

• Life: The most obvious is human touching wearing the features down or breaking them. Plants may also try to grow root systems and break stone features. Animals may alter the environment to make one of the other conditions worse. Let us not forget the threat of small minded idealist bent on destroying great works of prior generations.

Stone isn’t all its cracked up to be.

I think stone has its place in the archive of human knowledge. If picked correctly, positioned well and designed with care some simple ideas can be extended into the future by 10’s of thousands of years. The ability to store lots of information really isn’t there, and I would limit the amount of precise data I try to coax stone to keep. Stone might be a good choice for an intermediate storage media that tells the story of how to use a better one. For now I’ll call it a gateway media for Anticryptography.