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Forgotten and deteriorating, it lay for hundreds of years inside Týřov Castle in the Křivoklát region. It was only archaeologists who brought it back into the light of day. The late medieval hazelnut cracker, made of a copper alloy, was discovered during archaeological excavations in the 1980s. According to Josef Hložek from the Department of Archaeology at the Faculty of Arts of the University of West Bohemia in Pilsen, the nutcracker originated in Flanders or the area along the Franco-German border around the turn of the 14th and 15th centuries. “It is decorated with figures of hunting dogs and birds of prey. On the upper side of the jaws, there is a human face with eyes, a nose, and a wide mouth, a motif that was very popular from the Gothic period through to Art Nouveau. The small size of the jaws gives us an idea of just how much smaller hazelnuts were in the Middle Ages than they are today,” Hložek explained.

Experts from the RTI research center at the Faculty of Mechanical Engineering have now used 3D scanning and 3D printing to add the missing half of the nutcracker, restoring its original appearance after five hundred years. Václav Blábol, a student at the Faculty of Mechanical Engineering, also helped restore the historic object. He is due to complete his Master’s degree next year, but for now, he works in RTI’s workshop metrology laboratory, where similar replicas are frequently produced. As he told INFO.zcu in an interview, he enjoys working with historical artifacts.

How is a replica like this made? Does each artifact require a different approach?
It depends on the size, but the process does not differ very much. First, we need to place reference points on or around the object so that the scanner can orient itself. If the part is small, it is enough to place the reference points around it; for objects larger than ten centimeters, they are attached directly to the surface. The object is then positioned and scanned. Smaller objects can be completed in about ten minutes, while more complex parts may take up to an hour. This produces a point cloud on the computer, which can then be edited in various ways – for example, we can remove unnecessary parts of the scan, fill holes, smooth out irregularities, and so on. We then send the digital model to the virtual prototyping laboratory, where it undergoes a standard plastic 3D-printing process. It is printed, cleaned of residual powder, and then further finished using a plastic abrasive, producing a uniform, smooth grey surface. The West Bohemian Museum in Pilsen then applies a patina to the piece, making it virtually indistinguishable from the original.

Is there any difference between scanning historical artifacts and industrial components?
The basic principle is always the same. With artifacts, the most important thing is to capture the shape so that the most faithful possible replica can be printed from the data. With engineering components, on the other hand, exact dimensions are assessed. For example, we create replicas of machine parts for which the original drawings are no longer available. We have also made a grille for an older car model that is no longer manufactured, among other things. It does not always have to involve 3D printing, however – sometimes we also use the scanned data to machine a part on a CNC machine.

What do you enjoy more – taking measurements at companies or reverse engineering?
Scanning is actually the most enjoyable part. We get to handle specific components or historical objects and recreate them on a computer. When we prepare drawings for a company or process measurement data, it is essentially just sitting at a computer. So perhaps the biggest advantage is the variety of work. Replicas also work very well during tours for schoolchildren or parents with children, because they allow us to explain the principles of our work in an accessible way and show them actual objects. In commercial projects, this is often not possible due to confidentiality agreements.

Does working in the laboratory help you with your studies?
Some people say that a degree is just a piece of paper. I do not entirely agree. In the laboratory, I can try out many things in practice and learn how they really work. I have found that I enjoy this field and would like to continue working in it. My Master’s thesis is also focused on scanning – specifically, I am comparing whether it is better to scan objects after applying a special matting spray or without using any spray at all.

The RTI center has been producing replicas of historical artifacts for several years. Museums and castles are interested in them because visitors no longer have to view exhibits only behind glass, but can also touch and handle the replicas. For this reason, custom production for selected museums is also being considered in Pilsen for the future. Almost 20 replicas have been created so far at the UWB Faculty of Mechanical Engineering. For example, copies of two stove tiles from Kyšperk Castle, dating to the second half of the 14th century, are currently on display at the National Museum in Prague. The completed nutcracker from Týřov will be exhibited next year, successively, at the West Bohemian Museum in Pilsen, the T. G. Masaryk Museum in Rakovník, and Křivoklát Castle.