Soft white with fine structures, slightly transparent and shimmering: the special appearance of ivory has been difficult to imitate so far. But now researchers are presenting a convincing and practical imitation process for ivory, with which above all old art objects can be restored with high precision: The elephant-friendly material “Digory” can be quickly transformed into replicas of highly complex carving art using a 3D printing process.
The natural product is taboo! Thousands of elephants are still illegally killed every year because of their tusks – at least officially, an international ban on the ivory trade has been in effect since 1989. For art lovers and especially for restorers, however, this poses a problem, because the beautiful material was known to have been used for centuries for the production of objets d’art. By doing without the natural substance, they now have to resort to substitute materials in order to restore or reproduce ivory parts of old art objects.
But bones, mussel shells and plastics have not yet offered any really satisfactory solutions. Because they usually do not have the optical features and material properties of the prototype and the objects have to be laboriously made by carving. On the other hand, manufacturing options using 3D printing would be ideal. However, objects with convincing ivory characteristics cannot be made from the plastics available to date. But as an Austrian development team reports, they have now succeeded in mastering this challenge.
“Digory” – the practical alternative
“The research project began with a valuable 17th century shrine in the church of Mauerbach,” explains Jürgen Stampfl from the Vienna University of Technology. “The art object is decorated with small ivory ornaments, some of which have been lost over time. So we were asked whether the complex parts could be replaced with 3D printing technology. ”Despite the team’s experience with this process and ceramic materials, it turned out to be tricky to produce good imitations. “With our 3D printing systems, we process different material formulations for very different areas of application, but this project was something new for us too,” says co-author Konstanze Seidler.
As the experts explain, a number of requirements had to be met at the same time. Because the material should not only look like ivory, but also have a comparable strength and rigidity, so that later reworking is possible. But as the researchers report, through numerous experiments they finally succeeded in finding the right mixture for a material that can be used in conventional 3D printers based on the stereolithography principle. The basis is formed by calcium phosphate particles with a diameter of around seven micrometers, which are mixed with extremely fine silicon oxide powder with a special resin. “The aspect that ivory is translucent was particularly tricky,” reports co-author Thaddäa Rath. “Only if you use the right amount of calcium phosphate will the material have the same translucent properties as ivory.”
Fix printed ivory art
The new material is processed in 3D printers using the so-called hot lithography process. Using a computer model of the prototype, the substance is cured to the desired shape using a UV laser. The complete object is thus created layer by layer within a few hours. By subsequent analysis of the results from the material called “Digory”, the researchers were able to prove that it has both optical and material properties that correspond to those of ivory. “The result shows once again how diverse the possible uses of stereolithography are,” says Seidler. After production, the color of the object can still be adjusted as desired – for example to make it appear old. Among other things, the use of black tea achieved good results. The researchers report that the characteristic dark lines, which normally run through ivory, can also be reproduced true to the original.
As you finally emphasize, the development is a major step forward in the field of restoration: With Digory, a better, more beautiful and easier to process substitute for ivory is now available than before. Instead of laboriously carving out complex objects from the previous replacement materials, you can now simply print them out in a few hours. The team hopes that the new material will therefore prevail – as an aesthetically and mechanically high-quality ivory substitute for which no elephant has to die.
Source: Vienna University of Technology, specialist article: Applied Materials Today, doi: 10.1016 / j.apmt.2021.101016