We are artists/conservators at one of the largest museums of fine art in Europe. As museum conservators, we have decades of experience in studying and investigating the techniques and technology of painters of all periods. We examine the structure and methods of applying prime coats, subsequent layers of paint and the structure of the brush strokes. The scientific copying of an original painting is one of the fundamental disciplines of the comprehensive study of painting techniques at our Art Conservation Department.

Before the department begins work on a copy, the restorers examine the original painting under a microscope, determining the composition of the paints and pigments, the sequence of the brushstrokes, previous restorations, etc. They study how the artist prepared the canvas prior to beginning work. They examine whether the artist touched up the underpainting and how the effect of luminescence was achieved.

All these investigations help our talented artists/restorers to produce an absolutely identical replica of the original. They even attempt (if appropriate) to convey the effect of a coat of yellowing varnish or the darkened texture of the paint, in imitation of the original. The objective is to achieve such a likeness that not even a professional can visually distinguish the copy from the original.

The process begins when the original painting is transferred from the museum depository to the conservation laboratory, where microscopes and special analytical equipment are on hand. If the original hangs in an exhibition hall, the artist/restorer copies the original in situ.

The most complicated tasks are also the most interesting, particularly when a new approach or an unusual solution is required. Such complexities often present the artist/restorer with a real conundrum, especially if there is an intricate composition with a large number of figures or a complicated palette (what was the sequence in which the figures were added or the paints applied?). Unruly, unpredictable and expressionist brushstrokes provide another challenge. This dedication to perfection requires an enormous amount of time and patience, but the results speak for themselves.

In the process of reconstructing the original technique of each individual painter, we do not use the fabric primed canvases sold in special artists' shops. We prepare each canvas individually, using 100% linen canvases in exact accordance with the texture and thread structure of the original. We stretch the canvas onto a wooden stretcher and paste it several times using special glue. After the glue has dried, we apply a prime coating based on historical methods.

We try to make the surface identical to that of the original painting. In order to do so, we either create a thoroughly polished ground surface completely covering the structure of the canvas threads (particularly good when imitiating works painted on wood) or a thin ground only partially concealing the texture of the canvas. The colour of the ground is also extremely important. It has to be identical to the original. We make it coloured if our investigations show that the painter did it this way. The ground of Isaac Levitan's Moon. Twilight, for example, had a blue tinge. Here is how we did it..

It is also extremely important to follow the exact same order and procedure of work as the original painter. We do the drawing and touching exactly as it would have been done by the master. We first draw the whole picture, right down to the smallest details, in brown oils and white.

The resulting picture looks like the finished work, only in 'black-and-white' (named 'grisaille'). It is a pity that the observer will never see this part of work, which will later be covered with coats of paint. But we do it all the same, because this is the key to the accurate conveying of all the hues of the surface, based on an exact reproduction of every layer of paint applied by the master. A new layer of paint is often applied as a semi-liquid, transparent coat, in order to bring out the colour of the paint in the layer immediately beneath. Thickened linseed oil is used here, helping to recreate the depth and transparency of the layers of paint. The contrast between the textural and volumetric application of the paints on the light sections of the picture and the thin, semi-transparent shades creates a thrilling play of different tones. This is the magical moment when the lower layers of grisaille start to perform their role, creating the fantastic effects of luminescence and depth.

And that's not the end of the story! When all the upper layers of painting have completely dried, we apply a new semi-transparent coat of paint, making it look as if our painting was actually created many decades or centuries ago. The only thing we do not do is create artificial craquelure, as this would be going too far. We have to be very careful not to cross the thin line dividing a first-rate copy from a clever fake! Neither do we ever attempt to age the verso of the canvas or the stretcher.

If the original artist did not cover his masterpiece with a layer of varnish, we also recreate an unvarnished, matt surface. Every painting demands an individual approach and each stage in this painstaking process is unique. The most important thing is that our finished copy evokes the exact same feelings of delight and rapture as the original masterpiece. Then we have succeeded.

The greatest pleasure for us is the when we submit our copy to the special Expert Copy Commission, which compares our creation to the original (this is always done on the completion of each work). Very seldom can the members of the commission immediately distinguish between the original and our replica. Only the slight obligatory difference in size and the absence of a signature on the facial side shows which work is the copy. The astonished faces and enthusiastic conclusions of the commission members are the best reward of all in our complicated yet fascinating job of reconstructing a painting by a Great Master.