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Colour Research

Influence of the three colour dimensions and colour distortion phenomena

Our visual perception is strongly influenced by the anatomical structure of the eye and by lighting conditions. While looking at the painting, we perceive existing colour attributes, using retinal photoreceptors – cones – that serve our vision at higher luminance levels. Lighting, on the other hand, affects our colour discrimination as well as our perception of three dimensions of colour. During the retouching process our visual system can be affected by multiple optical impressions that many painting conservators are not fully aware of. Colour distortion phenomena can impact our observation stealthily, while producing simultaneous contrasts and afterimages that interfere with our colour discrimination as well as our decisions in pigment mixing. Our aim is to analyse these optical properties and to provide practical guidelines that will minimize colour distortion. One of the proposals is the use of 18% reflective grey card to cover adjacent colours around the paint loss. This method can be adopted as a helpful implement for tuning our colour perception.

Farnsworth-Munsell 100– hue test

The matching colour in retouching depends on the ability of the observer to differentiate colour. This ability was measured on 28 volunteer conservation students of varying aged using a specific test of colour discrimination – the Farnsworth-Munsell 100-hue test. Fourteen of the subjects were aged between 18-28, six between 29-38, seven between 39-48, and one was over 49 years. 50% of subjects showed a wide-ranging ability to differentiate colour: none of them was colour blind. 7% of the students, however, have low ability to discriminate hues but only one was aware of his deficiency. Our aim is to reveal the importance of this test for the conservators, using it as a detector to select eligible subjects with high sensibility in colour discrimination, which is an essential predisposition to perform accurate colour matching in retouching.

Mimetic reintegration of complex losses

There are many manners to look at the painting and the way the artist has conveyed his subject. In thorough visual examination we perceive the elements of art captured on the surface, such as line, shape, colour, mass, volume, texture and perspective. However, digging deeper, through the use of technical studies, we are introduced to a painting’s inner structure, usually compound of multiple layers hidden beneath. Mimetic reintegration of complex losses requires the understanding of both of these aspects in order to recover the artist intention with as much accuracy as possible. This study explores the main stages of preliminary research in retouching Old Masters paintings. It aims to make evident the importance of technical and historical information usually gathered in the conservation-restoration process, and elaborate their application in mimetic retouching of the paint layer. In this context, and in collaboration with the painting conservator Sandra Sustic, there are consider several interesting case studies carried out at the Croatian Conservation Institute and Arts Academy of the University in Split.

Colorimetric analysis of two watercolours used in retouching

Prussia blue and phthalo blue have a particularly importance in retouching because they provided a considerable amount of green and they are also transparent, which will give strong clear greens when needed during the retouching practice. The objective of this experiment is to evaluate the colorimetric change of the two cited pigments, in watercolours, after being exposed to direct sunlight for one year, comparing the results with another two samples protected from solar radiation, and also analyse the spectral curves similarity between both. The pigments are of the brand Artist´s Watercolour of Winsor & Newton. Colour variations were determined in the uniform colour space called CIELAB. The results show that phtalo is more stable than Prussian blue.

Characterization of losses for the chromatic reintegration process

This study was conducted in the framework of the doctoral program in Cultural Heritage, specialization in Painting, which took place at the Catholic University of Portugal, with the theme of quality in chromatic reintegration. The aim of this research is to propose a system for the characterization of the losses in the pictorial surface, so that conservator-restorer can have access to qualitative and quantitative accurate information before, during and after the intervention. We used photographic images and a geographical information system software, used in the processing of spatial data, the QGIS open source program.

Retouching with mica pigments

Mica pigments are defined as a type of the interference pigments with high reflective and refractive properties. Due to their ability to generate a remarkable array of colours, these pigments have become an additional material on the retouching palettes of conservator-restorers, in particular for reconstructing the losses of metallic surfaces. However, their feature to manipulate incident light can produce large colour shifts depending of the viewing angle and illumination settings. This research is based on bibliographic study and optical observations of mica pigments in retouching. It aims to enhance conservators understanding of these materials in order to get more accurate colour matching results. One of the main factors that need be taken into account during retouching, are selection of pigments of the same geometrical structure, as well as the constant source of illumination.

Nine colours palette

The selection of the most suitable colours for retouching practice is usually not an easy matter to settle. In order to use a restricted palette, many conservators choose to use the three primary colours, realizing in short term that each paint brand has its primary colours and with each set of three colour-pigments may obtain only a limited range of tones; additional tints are normally required for tones outside this range. The aim of this study is to propose an alternative system, based on rules of colour theory, which consists of nine colours, two yellows, two blues, two reds, the white, black and the burnt umber, using the Artist´s Watercolours from Winsor&Newton.

My Tools

Art Pigment Database
Probably the most complete color index pigment code reference of it's type available on the internet for free. The pigment information is sorted by color index name making it easy the look up the pigment codes that are listed on artist paint tubes.





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Nine colours palette
The selection of the most suitable colours for retouching practice is usually not an easy matter to settle. Our propose is based on rules of colour theory which consists of nine colours: two yellows, two blues, two reds, the white, black and the burnt umber, using the Artist´s Watercolours from Winsor&Newton.




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Golden Paints Mixer
Golden Acrylics have developed a free, fun, online tool to help artists with colour mixing. The Golden mixer was based on data captured from actual paint mixtures using Golden Heavy Body and Fluid colours. The colour data was captured using a spectrophotometer on .01" thick paint films over black and white areas of test cards. The aim of MXR is provide a starting point to get you to the colours you want more quickly, not a final or perfect formula.
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QGIS
QGIS is a cross-platform free and open-source desktop geographic information system (GIS) application that provides data viewing, editing, and analysis capabilities. GIS technology can be a useful tool for conservators-restorers and all other categories of experts involved in cultural heritage activities




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