EP2176646A1

EP2176646A1 - Method for non-destructive surveying in depth of stratified bodies

Info

Publication number: EP2176646A1
Application number: EP20080776556
Authority: EP
Inventors: Anna Pelagotti
Original assignee: Art-Test Di Luciano Marras & C Sas; Art Test Di Luciano Marras & C; Art-test Di Luciano Marras E Anna Pelagotti SNC
Current assignee: Art-Test Di Emanuela Massa E C Sas
Priority date: 2007-07-11
Filing date: 2008-06-30
Publication date: 2010-04-21
Also published as: ITFI20070156A1; WO2009007872A1

Abstract

A method for non-destructive surveying in depth of stratified bodies (11) comprises the stages of irradiating the body (11) with at least one form of radiation (3) capable of reaching at least one deep layer (1,10) of said body, detecting the radiation (4a) emitted by or reflected from the body (11), and processing said radiation emitted by or reflected from the investigated body.

Description

METHOD FOR NON-DESTRUCTIVE SURVEYING IN DEPTH OF STRATIFIED BODIES

* * * * *

FIELD OF THE INVENTION The subject of the present invention is a method for non-destructive surveying in depth of stratified bodies.

The term stratified bodies is used herein to indicate all works, paintings but not exclusively so, with a layer of potential interest located deep down with respect to the visible surface layer, and more generally those components, such as for example the epidermis, where st is useful to be able to investigate the characteristics of underlying layers not distinguishable by visual inspection.

DESCRIPTION OF THE PRIOR ART

In the artistic heritage protection sector, stratified artwork surveying methods are known by means of which it is possible to analyse underlying layers using, for example, irradiation with infrared light, or by means of sampling operations.

The infrared radiation technique allows non-destructive viewing of the layers underlying the visible surface. Using this method, it is possible to identify the artistic and operational techniques of the artwork, for example distinguishing the areas of a preparatory drawing performed freehand from those achieved using transfer techniques.

RECTIFIED SHEET (RULE 91) ISA/EP However, the infrared light analytical technique is not without drawbacks.

A first drawback resides in the fact that the infrared rays generally pass through the varnish layers and the pictorial layer, indistinguishatøy, hence not permitting the collection of information specific to each of them. A second Known analytical method consists of performing sampling operations in defined parts of the art work, by means of which it is possible to analyse the individual varnish and pictorial layers overlying the art work itself.

However, even this technique has certain drawbacks. A first drawback resides in the fact that this technique is invasive, since in order to execute it, it is necessary to take an actual core sample from parts of the painting.

This drawback is much more significant, since besides being invasive, this technique only allows the analysis of small parts of the art work, and so it is very difficult, if not impossible, from the results thus obtained, to achieve an overall reconstruction of the individual layers over the entire painted surface.

SUMMARY OF THE INVENTION

The scope of the present invention is to obviate the above-mentioned drawbacks by providing a method for non-destructive surveying in depth of stratified art works.

This scope and others still, which will become clear over the course of the following detailed description, are achieved, in accordance with the

RECTIFIED SHEET (RULE 91 )

ISA/EP present invention, by a method for non-destructive surveying in depth of stratified art works having technical characteristics in accordance with the appended independent claims, in addition to further embodiments of the same being identified in the appended and corresponding dependent claims.

A first advantage of the invention consists of the use of a fluorescence technique for deep surveying.

This survey technique, entirely known in the art, exploits an intrinsic property possessed by many artistic materials; namely that different materials, even if visibly identical in terms of colour and appearance, possess different chemical characteristics and thus different fluorescent light emission properties, if subjected to irradiation with UV light.

Thanks to the method of the invention, use of the non-destructive fluorescent technique has been made possible in order to obtain separate information on the surface layers and materials deposited deeper with respect to the visible layer, for example the pictorial layers of a painting covered by other more recent coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in further detail below with the aid of flhe attached figures, representing a purely exemplifying and non-limijing embodiment wherein:

- figure 1 schematically outlines certain stages of the method according to lh® invention.

RECTIFIED SHEET (RULE 91) ISA/EP DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the appended figures, a method for non-destructive surveying in depth of stratified bodies 11 is described comprising a first surface layer 2 and at least one second underlying layer 1 or 10, that is invisible and generally capable of fluorescing if reached by suitable radiation.

Dn one example embodiment pertaining to surveying art works according to the method, UV radiation 3 is irradiated over a stratified work 11 at such an angle of incidence and wavelength as to reach the deep layer 1 , constituted, for example, by the pictorial layer of a painting.

Due to the effect of the incident radiation 3, the fluorescent component of the layer 1 emits fluorescent light 4 characteristic of the material making up the layer 1 or 10. The fluorescence originating from the deep layer or the radiation emitted due to the fluorescence of the more superficial layer and reflected in a characteristic manner from the layer in question, crosses the overlying layer 2 so as to then be detected and analysed by a detection device 6, for example a CCD sensor connected to a processing unit 9 for the analysis of the signal detected. According to the invention, detection of the tight reaching the sensor is performed by distinguishing ihe emitted or reflected component typical of the material forming the layer under investigation 1 or 10 and not filtered by the layer 2, from in© other components that might reach the sensor 6,

RECTIFIED SHEET (RULE 91) ISA/EP for example ambient light 8 and components due to reflection from the surface of the visible layer 2 of light originating from outside.

In the explanatory example of figure 1 , UV radiation 3 is emitted by a corresponding UV source 7, advantageously, a high-pressure mercury vapour discharge type, but it should be understood that various emission sources may be used.

Again, with reference to the outline shown in figure 1 , the deep layer 1 emits fluorescent light 4 split into at least two distinguishable components:

- a first component 4b constituted by a portion of the radiation 4 absorbed by the surface layer 2: and

- a second component constituting the radiation of interest 4a originating from the deep later under examination 1 .

According to one preferred embodiment of the method, the detection of the radiation emitted or reflected 4a from the deep layer 1 , is multispectral in nature and is implemented by alternating a plurality of interferential filters 5 interposed between the emitting layer 1 and the detection device, for example a CCD sensor 6.

Through alternating interpositioning of the filters 5, it is possible to obtain distinct images for each individual spectral band used.

According to the method, by means of the filters 5, the wavelength of the radiation emitted from the body under investigation and reaching the sensor, typically in the range between 350 nm and 800 nm, is selected, and it is possible to associate a depth value for the emitting layer 1 to be analysed with the radiation wavelength value.

Thanks to the invention, it is thus possible to associate an emitting layer depth with a pre-determined wavelength, in such a way as to be able to isolate the radiation originating from this individual layer and then "flip through" the body, discriminating the different wavelengths in order to allow the non-destructive surveying of the individual deeper layers.

The images obtained from each individual layer using the sensor 6 are then transmitted to the processing unit 9 advantageously together with the multispectral images obtained with the same devices, but by illuminating the body with white light. The unit 9 can thus process the signals acquired using appropriate processing algorithms in order to isolate the portion of the radiation 4a characterising the deep layer 1 .

Advantageously, the images obtained may be subsequently reprocessed in RGB trichromy (RedGreenBlue).

The analysis method according to the present invention also includes a calibration stage, by means of which it is possible to isolate the fluorescence signal from the parasitic visible light emitted from the lamp and reflected by the surface of the painting.

The invention delivers important advantages, first of all, the ability to non- destructively analyse the composition of the individual layers underlying the most superficial layer of a painting, or stratified body in general.

In the description of the invention, reference has been made to surveying fluorescence emission within the visible spectrum, excited within the UV range, or rather the use of incident UV radiation to induce the deep layers to produce analysable visible fluorescent light.

This is because it has been found that the UV radiation, although characterised by low wavelengths, due to its high energy content, is particularly advantageous and effective at reaching the deep layers. However, remaining within the scope of the invention, also according to the physico-chemical characteristics of the material under investigation, it is possible to use radiation within the visible range to induce the deep layers to produce fluorescence emission, still in the visible range. The invention has been described with reference to a preferred embodiment, but it is understood that equivalent modifications may be made without therefore departing from the scope of protection granted by this industrial patent.

Claims

1- Method for non-destructive surveying in depth of stratified bodies (11) characterized by the fact of comprising the following stages:

-irradiating the body (11) with at least one form of radiation (3) capable of reaching at least one deep layer (1, 10) with respect to the surface layer (2) and comprising fluorescent material, with the aim of eliciting emitted or reflected radiation (4) from one or more of said layers

(1, 10);

•detecting said radiation (4a) emitted by or reflected from said body (11), discriminating the radiation emanating from the body (11) according to wavelength,

-associating a depth value for a layer (1 , 10) to be investigated with a discriminated radiation wavelength.

2- Method according to claim 1 wherein said surveyed layer (1 , 10) comprises fluorescent material and said discriminated radiation is fluorescent light emitted by said layer (1 , 10).

3- Method according to claims 1 or 2 wherein said discriminated radiation is fluorescent light reflected from said layer (1 , 10).

4- Method according to any of the preceding claims wherein said radiation wavelength discrimination stage is multispectral detection.

5- Method according to any of the preceding claims wherein said multispectral detection stage is implemented by alternating a plurality of interferential filters (5) interposed between the emitting body (11 ) and a

RECTIFIED SHEET (RULE 91 ) ISA/EP detection device (6).

6- The method according to any of the preceding claims wherein said detection of said discriminated radiation (4a) is performed using a CCD sensor (6).

7- The method according to any of the preceding claims wherein said radiation (3) is UV radiation.

8- The method according to claim 7, wherein said UV radiation is emitted from a high-pressure mercury vapour discharge UV source (7).

9- The method according to any of the preceding claims further comprising the stage of filtering said fluorescence so as to isolate the fluorescence itself (4a) from ambient light (8).

10- The method according to any of the preceding claims comprising a calibration stage.

1 1 - The method according to any of the preceding claims wherein said radiation emitted or reflected from said body (1 1 ) is discriminated into wavelengths selected from the range between 350 nm and 800 nm.

12- The method according to any of the preceding claims comprising a processing stage for one or more signals corresponding to said detection stages.

13- The method according to claim 12 wherein said processing stage is apt to isolate an image representative of the surveyed layer (1 , 10).

14- The method according to any of the preceding claims, wherein said body (1 1 ) is a painting, and said surveyed layer (1 , 10) is a deep pictorial layer.

15- The method according to any of the claims from 1 to 13, wherein said body (1 1 ) is a portion of epidermis, and said emitting surveyed layer (1 , 10) is a deep layer epidermal layer.