#33 Brunelleschi & The Dome IV

So what was the magic solution that Bruno brought to the Dome on August 7, 1420?

How do you build a dome out of bricks, that curves upwards, with no support, that won’t fall down?

Well he actually invented not one, not two, but a handful of new tricks.

And this is even BEFORE he invented linear perspective.

The first thing I want to talk about is called In Italian – (”Spina di Pesce”)  – spine of the fish.

In English we call it Herringbone

A Zig zag pattern.

His idea was to zigzag the bricks.

If you have all of the bricks lying horizontal, the forces are all pushing in a single direction.

But if you stick a vertical brick in there every few bricks, it pushes back on the horizontal forces.

If you climb the dome, you’re actually walking in between the inner and the outer domes.

And in certain sections, where there isn’t any plaster on the walls, you can actually see the zigzag pattern.

This was so original, Bruno not only needed to convince the board of the committee, he needed to convince the workers that it wouldn’t all fall down on them .

They were working 230 feet in the air.

If the bricks fell down on them, it was certain death.

How did he make them trust him?

That 12 foot high demo dome we talked about last time – in the car park of the Duomo museum..

Another thing is that if you could take off the outer layer of tiles and look at the dome brickwork, you’d notice that the Spina di Pesce patterns follows the dome around each side like a spiral – so it becomes a single dome, not 8 sides.

This apparently spreads out the forces, making it more stable.

Very stable.

Like Trump. A very stable genius.

Where exactly Filippo learned of the herringbone bond is one of the dome’s unsolved mysteries.

The herringbone pattern had of course been known to masons and bricklayers for many centuries.

The Romans made extensive use of something they called opus spicatum, literally “spiked work”

and the pattern is also found in the half-timbered brick walls of Tudor houses in England.

In both these cases, however, it is decorative rather than structural;

the Romans used it only in ornamental paving on the floors of their villas.

However – systems of interlocking brickwork similar to that in the dome can be found in certain Persian and Byzantine domes, which leads some scholars to think that Filippo may have visited these lands during his Rome years.

Another trick he used to make it more stable is that if you looked at the bricks from corner to corner you’d see they form a downward arch.

Higher in the corners, lower in the centre of each wall.

This pushes the weight downwards.

Like you pushed me downwards in Vegas.

But there’s another great story about the zigzag pattern.

I said earlier that when you climb up the staircase, some sections aren’t covered in plaster?

Well apparently that was deliberate.

In the sections that Bruno didn’t plaster over, the amount of mortar between the bricks is way too small to contain the forces of the bricks.

But in sections where the plaster has chipped away over the centuries, you can see the right amount of mortar has been used.

Bruno knew his successors would think he was demonstrating his techniques for them to learn from, but really he was cleverly ensuring that they would fail in their attempts to recreate his work.

Sneaky fucker.

But another question is how he got all of the sides to look even and meet at the top?

Imagine if you’re putting bricks on top of each other, with varying sizes of brick – handmade obviously – and you’re slapping on mortar in between them – over 4 million bricks, Weighing 40,000 tons, there are going to be variations in height.

Not to mention the angle of the bricks with a slanting wall.

How did he get it so even?

And The octagonal building the dome was going on top of unfortunately hadn’t been built precisely evenly.

People have wondered how he did this for centuries.

And in recent years, one guy thinks he worked it out.

His name is Massimo Ricci – he teaches architecture at the University of Florence and he’s been working on a model 1:5 scale for 30 years.

Longer that Bruno.

He published a book -Il fiore di Santa Maria del Fiore in 1983

In it he talks about a guy called Giovanni di Prato – aka Joe The Prat –  who, around 1425, five years after work began, wrote a critique of Bruno’s methods.

The only contemporary surviving account of the work.

Discovered in the archives in the mid 19th century but no-one really understood the importance of it until Ricci.

De Prato was Ghiberti’s deputy.

In his own right he was a  lecturer on Dante at the University of Florence,

And from the get go he didn’t like Bruno.

And he thought Bruno was fucking it up.

De Prato said Bruno wasn’t sticking to the original design, and the dome would fall down.

Turns out he was wrong on both counts – the finished dome is exactly to the original design.

And so far it’s still standing.

It was probably a matter of politics.

Team Ghiberti hadn’t had much to do – Ghiberti had actually been fired at one point, but was later re-instated, but with less responsibility.

When the project began, Bruno and Gibbo were BOTH called capomaestro.

Which I believe translates as master builder or master mason

Not to be confused with a caporegime, who is the head of a mafia crew

And both Gibbo and Bruno had to share the capomaestro’s salary of 6 Florins a month which wasn’t much

AND – the Opera del Duomo decided not to award the prize of 200 florins to ANYONE

Cheap asses

Even though Bruno’s design obviously won.

Now we mentioned earlier that Bruno must have been pissed when he was told he had to share the job with Gibbo.

But how do you think Gibbo felt?

He’s spent 20 years producing the masterpieces of the Baptistery doors.

Although the first doors weren’t even finished yet.

Not until 1424.

But he’s already celebrated as a genius.

Remember he let people into his workshop so they could see what was happening.

What’s Bruno done?

He has no architectural experience.

So Gibbo decided to bide his time, wait for Bruno to fail and then he’d say “I fucking told you so”.

He kept working on his doors and didn’t go to the building site much.

Instead Bruno flipped it.

A few years into the project, 1423, it was time to come up with a design for the wooden chains that would go around the brickwork.

A new prize was set up – 100 florins – for the person who came up with the winning design.

Why anyone would trust these pricks after they reneged on the last prize, I have no idea.

But anyway, the competition went ahead, Bruno and Gibbo and some others submitted their designs.

And Bruno won.

But then, when the timber arrived, cut to his specifications, Bruno suddenly feigned illness.

He said he had to stay in bed.

And Gibbo would have to build the chains.

Of course, he hadn’t shown Gibbo his designs for the chain OR the dome.

So Gibbo tries to get it all working.

He bases the chains on similar chains used in the Baptistery dome.

But Bruno’s model called for a more complex design in which the logs would be clamped together with special plates made from oak.

These had to be attached both above and below the junctions of the logs by iron bolts.

The logs would then be wrapped in iron straps to prevent the bolts from splitting them.

He stays in bed until Gibbo has finished the first three beams.

Then he makes a miraculous recovery.

He climbs up to the top, examines Gibbo’s work.

And says “tut tut, this is a fucking disaster – I’m going to have to take it all down and start again.”

Bruno’s salary was almost tripled, to 100 florins per year.

Gibbo’s remained at 36 florins until the summer of 1425, when his pay was suddenly suspended.

It was resumed six months later, but in contrast to Bruno, whose wages had increased, Gibbo remained on a salary of 3 florins per month.

This meant that after 1426 his work on the dome would earn him barely a third of what Bruno was paid—an indication of just how much he had been surpassed by his rival in the eyes of his paymasters at the Opera, who were paying him, in effect, a part-time wage.

So this di Prato guy was PISSED.

And di Prato might have been hoping he could get rid of Bruno and take over the project himself.

As part of his critique, he carefully sketched the rope lines Bruno was using to line up the sides.

And the work platform that his workers were standing on.

It was in the shape of a Flower.

Picture an Octagon.

Draw a Semi-circle from corner to corner.

The flower of the Santa Maria del Fiore.

What Ricci claims this is evidence of, is that Bruno Attached the rope line to the base of the work platform.

The other end of the rope goes to the top of the opposite wall.

Pull it tight.

Mark off where the bricks would be on the first wall and then make sure the bricks on the other walls are exactly on the marker.

It makes sure all of the bricks in the wall are lined up.

Move the rope around to the next section of the base, and the wall, and it will all be completely balanced and even.

Another trick Bruno came up with to prevent the bricks from pushing outwards – hoop stress – was to use iron chains that run around the dome like the metal rings around a wine barrel.

But as we can’t see them – they are hidden inside the brickwork – this is just a theory.

A magnetic survey of the dome in 1970 found no evidence for them.

He also used sandstone chains.

This chain was complex in design, consisting of two concentric rings of stone laid horizontally around the octagonal circumference of the dome.

These long beams rested on, and interlocked with, shorter beams laid transversely, like railway ties, at intervals of every three feet.

Along with the wooden chains, all of these are hidden from view.

The large white Carrara marble spines that run up the outside of the dome are also used to contain the hoop stress.

Another of the most obvious problems in building the dome was how to transport heavy building materials such as sandstone beams and slabs of marble several hundred feet above the ground and then place them into position with the accuracy demanded by Bruno’s design.

The sandstone beams weighed some 1,700 pounds each, and hundreds of them needed to be raised onto the cupola.

No known lifting mechanisms were capable of raising and maneuvering the enormously heavy materials he had to work with

To solve this problem Bruno was compelled to invent a totally new machine to move and carry tremendous weights to incredible heights.

The hoist that he created was to become one of the most celebrated machines of the Renaissance, a device that would be studied and sketched by numerous other architects and engineers, including Leonardo da Vinci.

The way people raised heavy stuff Up until his time, lifting devices were referred to as rota magna, the great wheel, a treadwheel crane, looked like a gerbil cage.

It had been around since ancient times.

In De Architectura – The Ten Books on Architecture –  the Roman architect Marcus Vitruvius Pollio aka Vitruvius describes a treadmill turned by “tramping men,” presumably slaves.

BTW Vitruvius dedicated the book to Augustus.

This work is the only surviving major book on architecture from classical antiquity.

It was rediscovered in 1414 by the Florentine humanist Poggio Bracciolini – who we’ll talk about in upcoming episodes.

It’s a shame he didn’t find it before Bruno had to go to Rome and figure it all out by himself!

Back to the big wheel.

The large wooden wheel was the size to support two adult men walking side by side.

The spindle went through the centre of the wheel and attached to ropes.

The rope went over several pulleys to an object such as a cut stone, attached to a wooden palette by ropes.

When the men walked, the wheel turned, the rope pulled over the pulleys, and the stone was lifted.

Bruno realises it wouldn’t work for the Duomo – it was too high. Too heavy.

So he Invents a new type of hoist that uses oxen instead of people.

They turn a wheel which turns a vertical shaft.

It in turn has a series of cog wheels which interlock, turn a drum which coils the rope.

But he knows they will have to lower things as well, so it has a reverse gear.

Two cogs – a top and a bottom.

The bottom one turns, the hoist goes up.

The top one turns, the hoist goes down.

The oxen can walk around and around all day long and the hoist goes up and down.

The exact inspiration for this remarkable machine remains as mysterious as that behind Filippo’s other inventions.

The specialist theoretical knowledge needed for constructing such a hoist was largely unavailable in 1420, though soon afterward a number of manuscripts on Greek mechanics and mathematics began arriving in Florence, putting architects and inventors of the Renaissance in possession of engineering techniques far beyond those available in the Middle Ages.