By Richard Baldwin
Preserving cultural artifacts always involves a balance between public access and maintaining the object itself. In recent years that balance has changed.
Non-contact metrology devices can capture the finest details of an object. We can create accurate 3D digital replicas which give opportunities for study and preservation that didn’t exist before. Scientists and historians can zoom right down to the micron level and examine the tiniest details. Every scratch, every chip and mark can give an insight. In this blog post we recall the fascinating project of scanning the bronze horses of the basilica in St Mark’s Square, Venice and we’ll look at how today’s technology would make the process much quicker and easier.
The project was so successful the same team came back on several occasions to scan other priceless objects. This website and video show the subsequent digitising of the beautiful altarpiece at the Il Tesoro di San Salvador church, also in Venice.
Digitising cultural artifacts is one of the most exciting forms of study and preservation because it allows us to get up closer than ever to priceless and fragile objects. It gives us a snapshot of their condition at a particular time and point of reference for future studies.
Earlier this year we reported on a digital twin and 3D printed replica of Michelangelo’s David, displayed at the Expo 2020 in Dubai. It was a project that took 2 people 10 days to complete because of the sheer size of the sculpture. When they finished, they’d completed the most detailed study of a renaissance sculpture ever undertaken. They saw traces left behind by the tools and the hands of da Vinci himself.
That project would have been far more complicated if the team hadn’t already built up a bank of experience in similar projects.
The horses of St Mark’s
St. Mark’s Basilica in central Venice (or the Basilica Cattedrale Patriarcale di San Marco in Italian) is one of the most important and beautiful places of worship anywhere in the world. It has a history dating back at least to the medieval period (AD 829 – 976), but the objects it contains go back much further than that.
St Mark’s Basilica, Venice
Among the treasures housed within the Basilica are four bronze horses known as the Triumphal Quadringa, or the Horses of St. Mark.
Probably dating from the second or third century AD, the Horses are at least 1700 years old. By comparison, Michelangelo’s David is relatively modern at a mere 517 years old.
They were already a thousand years old when they arrived in Venice after the sack of Constantinople in 1200. They survived civil unrest, looting, storms, floods, earthquakes, wars and only in 1980 were they finally brought inside from their position as guardians above the door of Basilica. The horses you see above the entrance today are replicas.
The study
In 2008 the Polytechnic University of Milan commissioned a study of the Horses to establish their preservation status. This would include a taking detailed scan and creating a complete 3D digital model.
It sounds relatively simple: go to St. Mark’s Basilica in Venice; set up the equipment (laser tracker and handheld scanner, laptop); scan the horses; home in time for tea. Not so.
Venice is most famous for one thing above all: canals. It’s quite possible to drive to Venice, but once you arrive you need to swap your car for a boat. In 2008 the amount of equipment required for a task like scanning the Horses of St. Mark’s Basilica filled a large MPV with no space left over. The laser tracker alone came in a box 4ft long and 2ft wide. Then there was a separate box for the tripod, and another for the controller, the cables, and computers.
If the same task were repeated today the equipment would take up less that half the space. Nowadays it all fits in just a couple of small boxes. The complete job took more than half a day. Now it would be done in half the time. The laser line on an AS1 scanner is 30% longer than the T-Scan model of 10 years ago. It weighs a third less too, which makes it a lot easier on the operator holding it up for hours on end.
In total around €200000 worth of equipment had to be loaded onto a boat and brought down Venice’s Grand Canal with locals and tourists looking on in wonder.
If that sounds like a challenge, imagine arriving at Puente Rialto and not being able to secure the boat directly to side of the canal. In true Indiana Jones style the intrepid apps engineers had to jump from one boat to another passing valuable metrology equipment to each other before they reached dry land.
Except for another complication. It wasn’t dry land at all.
The area is prone to flooding
It should be no surprise that Venice is subject to frequent flooding. At the time of the project, St Mark’s square was under 2 feet of water. Flooding is an increasing problem in Venice and when it happens the city authorities install raised platforms for public use. The team had to navigate all these obstacles with bulky equipment before they could begin the work at hand.
Tony Vianna was a member of the original team:
“Carrying all that equipment through St. Mark’s Square wasn’t easy back then. These days we’d have around 30 kilos less to take with us. The new AS1 scanners are 3 generations down the line and the technology has moved on massively.
“For example, the new equipment is much less sensitive to the surface you’re trying to scan. These objects aren’t a nice matt white, which would be ideal. They’re dark and metallic which absorbs a lot of the light or reflects in un-predictable ways so the laser from the scanner would get lost in the noise of the surface.
“The scanners we have today can scan shiny black surfaces as if they were matt white. The new scanners can easily move between different surface colours too. In the past you had to check the settings and the balance because different colours refract light in different ways. Now it’s all automated”.
In spite of all the challenges the team faced, they did a remarkable job and the results speak for themselves.
Detail from the original 3D model
This content was first posted on the Hexagon MI website.
