Ever since I read about the Sistine Ceiling at the age of 17, I was fascinated with the larger than life character of Michelangelo. I wrote elsewhere on this blog about his spiritual dimension but here I want to write about the technical marvel which enabled his artform to survive the centuries – thus avoiding the “second death” he feared – and that is, lime plaster.
Every civilisation on Earth independently discovered this complicated mechanism for themslves, and used it to various ends to leave their mark on history: Japanese, Indian, Chinese, Greek, Italian, Roman, even prehistoric. This is hard to explain unless we propose a model of intelligence in which intuition is a channel between nature and man; in such a model the surprising achievement of prehistoric man in isolating plants as medicines, insecticides and stimulants becomes comprehensible.
Genius, relying on a marvellously developed intuition, must have taken many forms in our ancient societies; intuition resembles the non-intellectual animal model of mind much more than we admit. Pets can sense when their owners are in distress, or when they are to arrive home at unexpected times, and wild animals can often sense impending natural disasters long before our most sensitive technology alerts us. An excellent book from the early 20th century called How Animals Talk illustrates and analyses such circumstances, but because these ideas suggest a much different form of mind than science can explain with its laboratory equipment, they are more or less forbidden. Add Darwinian randomness and bleak materialism and you have a dismal view of mind, a view dealt with at length elsewhere in this blog.
But the natural technology as used extensively in the Renaissance, and developed by the aforementioned multiple societies hinges on the unique property of what we call lime. The first stage in developing a lime plaster is to burn calcium carbonate ( CaCo3 ) – a product of billions of years’ worth of tiny life forms living and dying, commending their shells and exoskeletons to the Earth – leaving a powdery form ( CaO ) which has lost all its carbon dioxide. The second stage is to immerse this powder in water for an extended period of time – months, or even years – until, by soaking up the water, the powdered remains have turned into a soft clay-like substance called lime putty ( Ca(OH)2 ). The longer it soaks, the better a binding agent it is: the Romans even had a law that no lime could be used (for construction) unless it was at least three years old.
The qualities of this soft, clay-like material are extraordinary. When mixed with various aggregates such as sand or marble powder, lime putty acts as a binder, and the resulting mix can be spread on a wall where it returns to a hardened form by pulling CO2 from the air, becoming CaCO3 again. It allows the slow transit of moisture, so that no lime plaster can ever remain damp, and when slightly stressed, produces hairline cracks which heal themselves through an excess of free lime, instead of one almighty crack which brings the wall down.
When first laid on the flat surface, it can be painted with raw pigments; these are mixed in water to provide a transit. No binder like oil or egg yolk is needed; the plaster itself becomes the binder. What happens next is incredible: the plaster carbonates very slowly, and over the initial period of perhaps ten or twelve hours, the pigments are drawn beneath the surface, and covered with a carbonate sheen. At this point they become part of the stone: the plaster sets at a rate of about one millimetre per month and as it does so, the colours are united, darkened slightly, and their contrast softened so that the picture created survives the onslaught of time. This painting method is called fresco, which in Italian means fresh.
In Knossos, Crete, the Greeks painted cheerful bright blue dolphins which look the same today as they did then, more than two and a half thousand years ago. That is far beyond the capacity of modern chemical paint. The fresco paintings of Pompeii and ancient Rome are well known to us only because of this fantastic medium, as is the celebrated Sistine ceiling.
While sounding simple, the pitfalls of fresco are daunting. For one thing, every brushstroke laid on the stone remains in place, so that there is no question of adjusting your approach half way through or erasing a line once drawn. For another, you have a maximum of one day to complete the work in hand before the plaster carbonates to the point where it will not accept any more pigment. And since only certain pigments will withstand the corrosive action of the lime, and of direct sunlight, the painter is obliged to use mineral and earth colours, molecules which have already survived similar stresses within the Earth itself.
In most painting mediums, any oversight or error simply means scrubbing the work off or overpainting with something better; in fresco, you must get a hammer and chisel and remove the whole thing, an infuriating process. When Michelangelo experienced these difficulties, and more, he tried unsuccessfully to release himself from the contract, realising such a public failure would irreparably damage his career.
Since you can only paint a certain amount in a day the work is pieced together in sections, cunningly joined along edges of objects or changes in colour, so as to make the seams invisible. But the result, when carried out correctly, will outlast the artist and perhaps even the civilisation he painted for.
Having arranged an exhibition of paintings in a café here in Bedford and leaving via their courtyard, I was struck by the bleak appearance of a huge blank wall. The name of the café was Frescoes, so I dashed back in and proposed he install a fresco on his wall. He looked up with the expression of a man who had supposed he would not have had to see me again for at least another day. “And why would I want to do that?” Give me a day or two, and I’ll show you!
A quick session with photoshop in which I superimposed Michelaneglo’s Libyan Sibyl over the wall in perspective had him enthused enough to start a public subscription. By the next day the newspaper wanted a story and I was now obliged to learn a technique not widely practiced for half a millenia.
I knew nothing about fresco other than I had about 40 square metres to cover in winter, and that I was determined not to fail. I set to work ordering various kinds of lime putty and pigments, and experimented on tiles and roughened wood. I left these outside to see how they fared with the weather, and found no matter what I did, the plaster always developed hairline cracks which allowed the ingress of rain; they eventually fell to pieces. I thought it best to keep this research to myself.
What I wanted was a plaster made of Cararra marble, to get a brilliant white which lit up the pigments from beneath, but I noticed only sand plaster seemed resistant to cracking. Deciding the answer must be in the makeup of the grains, I examined electron microscope photos of sand and found that every grain was a different shape, varying in size from about 40 microns to about 850, or in other words one 25th of a millimetre to almost a millimetre.
The advantage was now obvious – if you jump into a beanbag full of identical beans, you can split the mass very easily in any direction. But if you fill it with all different size beans, there is now no consistent path of least resistance, and in fact if the variety in size was big enough, you would not be able to break the mass at all.
Marble powder had another advantage in that the pieces, cut by laser, were angular, which would make a much better tooth for the binder. So instead of using the standard 40 micron marble powder, I ordered every size I could get, with the largest being dolomite chips of 1200 micron size. I blended 45, 140, 355, 450, 800 and 1200 micron size chips, making what I expected to be a super-marble aggregate. I made my tests and sure enough, they didn’t crack – I then kept a plastered tile in the freezer to make sure it would survive freezing nights, as I had been warned that you can’t plaster with lime outdoors, and especially not in the winter.
The next morning confirmed what I had been told – the surface was covered with hairline cracks. But there had to be a way! I had read that Moldavian monasteries had outdoor frescos that had survived a thousand Eastern European winters. I know firsthand how cold those winters are. When I looked into the analysis of their methods, they seemed to have used things like straw and boiled porridge in the plaster, but most curious of all, they had added casein to the paint.
I started reading about casein and was staggered to find that this molecule, produced by mammals in breast milk, has some of the most unusual properties of any substance on Earth. Firstly, casein was enormous, at 25,000 – 35,000 daltons! It has a slight electrical charge in milk, and when it flows into a baby’s stomach, the hydrophobic outer portions form a solid ball holding the proteins and nutrients which can then be digested slowly by the stomach’s powerful enzymes over time while the baby sleeps.
Without this quadruple power of casein – flow generation, hydrophobic portions, clot formation and a fixed-rate susceptibility to enzymes, the baby would need to constantly feed as its stomach emptied, always using its energy up in the exertion of feeding, never able to completely stop taking in food for long enough to get substantial rest. This single molecule makes all mammalian life on Earth possible.
I found that it was so complicated that hardly anything is known about its structure: it has no fixed final shape, and only vague guesses have been made at the various types of casein and their inter-related functions. Doubtless they have the correct electrical properties on an atomic scale to hold nutrients within their shape, acting like a time-release capsule. But astoundingly, even though it retains the ability to allow water molecules to pass through – an essential property in lime plaster (and the lack of which in cement causes damp problems for every construction in the western hemisphere) once casein has set in the presence of air, it cannot be denatured through freezing or boiling. For all intents and purposes, it is indestructible!
Cennino Cennini mentions in his 15th century treatise that mixing milk with lime plaster makes it very strong, but he didn’t say how much was needed, and milk was not used in the Sistine, which is probably why it is covered with hairline cracks and much of it has actually fallen off – being replaced with repairs by lesser artists. God’s hand in one portion, and Adam’s hand in another – are all copies.
It also suffered when the building settled, but the smaller cracks are a result of the intonaco mix, and the heavy salt lines in his shaded areas show that moisture also collected wherever he used the thickest pigments.
I found adding as little as 2% raw casein powder made the plaster bunch up into clumps, but going up to 5% turned it into mercury – it ran everywhere as if it had a life of its own. Making a dozen different blends on a large board, after a few days the 5% casein mix which had been like soup, and would be impossible to work with on a wall, was solid as a rock. I tied to chip it off with a chisel, and found I could not dent it – I took a hammer to it, finding that the plaster was like diamond, absolutely solid, with the only difference having been a small increase in casein.
Now the question was how to blend this with my plaster – casein didn’t mix in water, but of course it did in milk, so to avoid using too much fluid (which would weaken the plaster when it evaporated) I made an 8x strength casein milk and added 1/8th as much. The plaster then became stodgy and stiff, which was to be expected, but then I added the same small quantity of ordinary milk at this final stage, which blended perfectly, added a small amount of extra casein, and loosened up the plaster so it was the perfect consistency.
The scaffolding arrived and was installed, and my plasterer and his team started drilling into the brickwork to mount the metal lath, a deadly razor wire assembly, when I got a call from Kevin, the manager. “This can’t happen,” he said. “I’ll lose my business. We can’t hear a thing when they drill! How many do they still have to do?” I asked how many he’d let them drill so far. “Two,” he replied. Then they only have 1,198 left! “They can drill after 4:30, maybe 5,” Kevin conceded, “or at weekends.”
The next call was from the plasterer, threatening to walk off the job. “We can’t drill at weekends because of the council – and we can’t set up and tear down every day to drill for an hour each evening – it will never get finished. I’m paying these lads per day, and we either start today or drop the whole thing.”
The only solution was for me to go down there and start drilling myself, from the very top of the building, and work our way down in the hopes people would get used to it, since nobody would dare tell me not to do it. Nobody was happy except us, but I think if it had been my café I would have said all the drinks are on the house while there’s noise. In Bedford, that would have permanently crammed the place full to bursting!
Anyway, such is life – after shredding my hands on the razorwire and drilling at least 500 holes myself, we had to mount the lath in reverse, that is, from the top down. But to our amazement, when we reached the lowest point, seven metres below, the last of fifteen rows of overlapped razorwire lath fitted exactly, within half a centimetre, to the existing space. Jim was incredulous. “This is impossible,” he pondered. Anyway, job done.
A couple of weeks ago I got the first painted bit on the wall, at the very top, in case anything went wrong, and that night the weather dipped below zero. Next morning I raced up four flights of scaffolding expecting to find bits all over the floor. But the thing was perfect – the colours were bonded, the plaster was smooth and cool to the touch, and there wasn’t so much as a hairline crack anywhere. A test sample proved so difficult to get off the wall a week later that we had to dig into the plaster layer beneath, leaving a crater to be filled in and evened out again. Far from the fragile liability everyone assured me, it is stronger than the building itself.
We’re about one third through at the moment, but my technique is getting quicker, and I hope to finish mid December – I have bruises all over my head from scaffold bolts, my clothes are ruined, my fingers are cut from the caustic lime and the cold, and the most convenient food for frozen fingers is chunks of Italian bread and cheese, with a little Frascati from time to time. I was never happier.