Painters from the Hermitage, world-famous museum of St. Petersburg, developed a new technology for restoration of art works, which were made of metal. The technology is based upon a recently developed compact laser, which became a reliable instrument in restorer’s hands.

Among other things, restoration of art objects, which are made of metal, includes elimination of various flaws, fractures, faults and caverns. Many art works are made by means of mixed technique or made of more than one material. Sometimes, masterpieces of old masters could not be taken to pieces, and a restorer faces a difficult task – remove fractures and flaws on one side of an item without damaging neighbouring fragments.

At different times different solutions for the described problem existed. Traditional techniques for fighting fractures were gluing or soldering. Reliable glues, made on the basis of epoxy resins, which are known to provide expected adhesive strength, appeared only in the second half of the previous century. They were widely used in restoration and did enormous harm, since their usage violated main principle of restoration – reversibility of materials, in other words, glue dissolution and returning glued item to its initial state. Soft solders are not always a solution, especially in case of dealing with precious metals. Unsolvable problems arise, when restoration of items, made of combination of metals with wood (weapons), leather (armour, hand bags), fabric, precious and semi-precious stones, is required. No glue or soldering is allowed in these cases. Restorers from the Hermitage found the solution – they used laser-beam welding with low-intensity lasers. Before using this technology on museum pieces, restorers for several years performed experiments, which resulted in optimal regimes of laser welding.

 

 

Coherent monochromatic laser beam, which has low angular spreading, provides high focusing accuracy and high energy concentration in strictly determined and very small work area. As a result, metal surface in zone of interest rapidly heats and then melts down. Fresh melting zone then rapidly crystallizes, and weld seam forms.

Another advantage of laser welding apart from high focusing accuracy is easy access to hard-to-reach places and heating a tiny working spot due to small diameter of laser beam without using any welding consumables. Moreover, laser welding causes no tension, which later can result in crack formation, and eliminates frequent companion of common welding process – weld seam corrosion. Gentle laser welding, which guarantees lack of damage for surfaces, which happened to lie close to restoration site, can be used for welding gold- and silver-plated metals without damaging the coating, as well as restoring museum pieces, made of combination of materials – metal and wood, metal and leather, metal and fabric, metal and precious stones, metal and enamel, various varnishes, paintings and etc.

Source: Science & Life

Kizilova Anna