Reproducing the Shilla Dynasty's direct-bonding granulation process

Granulation is a precious metal craft process method that decorates a metal surface using tiny metal granules. It was imported into Korea during the Shilla Dynasty around 1500 years ago, and many granulation ornaments have been found with the process's unique bonding features. The granules show a direct bonded interface with a neck. The key technology of making granules and bonding the granules is not well known. Thus, it is a technology of the Lost World. Although the exact bonding method is unidentifiable, it is known that the traditional method of preparing gold granules was time consuming and costly. Therefore, we proposed a process to reproduce the Shilla's granulation ornament using a modern method. First, we employed atomization to produce 22K gold granules. Direct bonding was accomplished using a spot welder and vacuum jig instead of using the traditional method of graphite bed melting and direct annealing. 0.8 mm granules were successfully fabricated and bonded directly to the substrate with a necking and 35% bonding ratio, which is very similar to Shilla's granule bonding. Moreover, to estimate the bond strength, K factors (fracture toughness index) at different bonding ratios were evaluated using a finite element method simulation. Our proposed direct bonded granule process and design were expected to have enough bond strength to be used as a key element for fine modern jewelry.