Digital restoration of a fragmented patera

23 Nov

The Regolini-Galassi tomb contained several outstanding silver and gold objects, now preserved in the Museo Gregoriano Etrusco in the Vatican.  One of the most interesting objects is a patera, in silver and plated gold, that was nailed to the wall of the tomb (see image below, showing its restored state, inv. nr. 20364) and that was uses for libation offers in religious rituals.  This patera most probably broke in pieces when being hit by stones from the collapsing roof in the cella of the tomb.

silver patera

Restored silver and gold patera from the Regolini-Galassi tomb (photo:Daniel Pletinckx)

silver patera - detail

Detail of this silver patera showing the nail hole and the deformation of the pieces (photograph: Daniel Pletinckx)

This patera is one of a set of silver objects from this tomb that are being produced in a Phoenician style with Egyptian decorations.  A very similar patera is preserved in the National Museum of Antiquities in Leiden, the Netherlands, and has been integrated in the exhibition “Etruscans: Emminent Women, Powerful Men” next to the Etruscanning VR installation that shows the virtual Regolini-Galassi tomb.  The provenance of this patera is unknown but scholars believe it originates from the Etruscan Barberini tomb, that has been excavated in 1855 and is dated around 630 BC.

Patera and lebes

Patera and lebes in the Leiden exhibition on the Etruscans (photo: Daniel Pletinckx)

patera RMO Leiden

Etruscan patera in Phoenician style in RMO Leiden (photo: Daniel Pletinckx)

As all objects in the 3D virtual reconstruction of the Regolini-Galassi tomb are visualised in their original state at the closing of the tomb, extensive digital restoration is needed for most objects.  As the 3D visualisation of the RG tomb happens in real time, and as we want the digitally restored objects to have very fine detail, we developed an innovative digital restoration technique that can be applied to most of the objects of the tomb.  This technique simulates the surface details of the objects (such as engraving, embossing, …) and turns them into a very efficient visualisation that can be used in real time systems.

So, let’s have a look at the digital restoration of the above mentioned patera.  We start with the drawings by Grifi in 1841 of the first restoration of the patera and an improved restoration by the restoration labs of the Vatican Museums in 1999.

drawing

Drawing of the first restoration of the patera by Luigi Grifi, 1841 (image: Vatican Museums)

patera restoration by Grifi - 1841

Drawing of the first restoration of the patera by Luigi Grifi, 1841 (image: Vatican Museums)

Improved restoration 1999

Improved restoration by the Vatican Museums, 1999, drawn by L. di Blasi (image: Vatican Museums)

When comparing both restorations, one can see that there are slight differences between these restorations but also that the 1841 drawings show more details than the 1999 restoration.  Possibly, some detail was lost in the first restoration or in undoing the first restoration.  When analysing the engravings, one can see that several motives are repeated one or more times, so that nearly always we can find information about missing parts by looking at other instances of the same drawing on another place of the engraving.  When doing so, very little uncertainty is left what to fill in, only a few details such as a bird or a tree have been filled in by analogy. We also compared closely with the similar patera from RMO, shown above, to come to the most probable digital restoration of the engraving (see drawing below).

Digital restoration

Digital restoration of the engraving of the patera (Visual Dimension)

In a second step, we simulated the production process of the patera by creating a displacement map from this engraving.  This displacement map shows as a black and with image the small height perturbations that are created by the engraving (and subsequent deformation of the metal around the engraved lines) on the front of the object and the embossing (created by hammering from the back of the object).  The embossing is created manually by simulating the impression of the blunt chisel, after studying carefully the high resolution images of the object (see image below).

Detail patera 20364

Detail of the patera with appropriate lighting to enhance engraving and embossing (photo: Vatican Museums)

All these different processes yield different displacement maps which are composed as layers in Photoshop.  The resulting displacement map is a  precise simulation of the relief of the complete, undamaged patera (see image below).

displacement map

Simulated displacement map of the whole patera (Visual Dimension)

The Etruscanning VR application uses Unity 3D as software to create and visualise the virtual tomb with its animated objects and narrated stories.  In Unity 3D, a displacement map can be transformed into a normal map, which allows to visualise very efficiently the relief of objects.  In this way, we visualise details of less than 1/10th of a milimeter on the surface of this object through a very lightweight 3D object (together with 80 other 3D objects) in a realtime system, running on a small, cheap computer (in our case a  Mac mini).  On the other hand, displacement maps are an optimal and easy approach for digital restoration.

reconstructed patera

3D visualisation test of the digitally restored patera (CNR-ITABC)

In the Leiden exhibition, the digitally restored patera can be confronted with the similar patera from the Barberini tomb, on display next to the VR installation, showing the added value of digital museum objects.

This blog is part of the Etruscanning project, that is been funded with support from the European Commission. This blog reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

 

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3 Responses to “Digital restoration of a fragmented patera”

Trackbacks/Pingbacks

  1. The Etruscanning application at ArcheoVirtual « Virtual reconstruction of Regolini-Galassi tomb - November 23, 2011

    […] continues to improve the digital museum objects through digital restoration and image based digitisation.  The Dutch version of this improved application will be installed […]

  2. The situla restored digitally « Virtual reconstruction of Regolini-Galassi tomb - November 27, 2012

    […] most efficient technique to deal with embossed and engraved objects (see also our blog post on the digital restoration of a patera).  In Photoshop, we created extra layers on top of the unwrapped situla decoration image, one […]

  3. The holmos and lebes digitally restored « Virtual reconstruction of Regolini-Galassi tomb - November 28, 2012

    […] the unwrapped texture, completing the missing parts.  Then, we painted the embossed features in a similar way as the other objects, through observation of those features on the many photographs […]

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