For those who take the 5 days training course on multispectral imaging and technical 2D and 3D photographic methods it’s provided a free RTI training spheres set. It is composed of 4 spheres (diameter 14 mm, 6,5 mm, 3 mm,1 mm). These are designed for close up and macro RTI and are suitable for RTI applications as reported on this paper “Macro Photography for Reflectance Transformation Imaging: A Practical Guide to the Highlights Method”.
This post “rti reflectance transformation imaging tips and tricks” gives a brief introduction to the RTI method. It is a growing community who is getting interested to the application of this very low-cost imaging tool for art examination; we just had a meeting in Cyprus, early this June, “Reflectance Transformation Imaging (RTI) and Cultural Heritage: Its Current State and Potential Future”.
The RTI method just needs black reflective spheres to be implemented. Though, to actually find suitable ones takes some time and effort. That’s the reason why this set of RTI spheres it is well appreciated. Furthermore, the bottom of the spheres has been flattened so that it is easy to put them in place and have them to hold the position. These spheres are intended for RTI images acquisition from the top with the object laying on a flat surface. Since these spheres are made of glass or metal cutting them is a bit of a work which I can do on my workbench but, I understand not everybody is practical with these kind of tools.