ABSTRACT
This chapter presents five figural situations to 120 observers in such a way that each of them would have to deal with only one figure of the series, and each figure of the series would be submitted to 24 observers. A case of transparency obtained without the use of different coloured surfaces, but only with means that are part of the practice of line drawing, is connected to a discussion raised by F. Metelli in the last section of his article “On the analysis of the phenomenal appearances of transparency”. The tests carried out would suggest that an important condition for opaque transparency in situations like the would be the characteristic of representing “a thing”, or “a solid object”, as a property of the figure located behind the transparent medium. Responses in favour of transparency were always very clear and immediate.
