Validation is an ongoing process for any scale, and thus also for the Vienna Art Interest Art Knowledge Scale (VAIAK). In this paper, we add to this process by assessing the validity of the VAIAK by using an itemresponse theory (IRT) approach combined with a qualitative approach to further understand the underlying process as to how participants answer. Our results show that both the art interest and the art knowledge scale can capture a range of ability in their respective domains and that the individual items have adequate discriminability and a range of difficulties. In addition, as expected, experts consistently showed higher levels of ability (in both interest and knowledge) and tend to find the items easier. Some items, however, exhibited differential item functioning, the implications of which (especially for the scoring of the scale) are discussed in detail. In combination with the qualitative analyses, one item (B6) was identified as an item that should be altered for which we propose the new "VAIAK-R." Furthermore, the qualitative analysis for the open items indicated that participants seem to use whatever knowledge is available to them to try to identify the correct answer, whether this is done by simply naming an artist or style that they know in either a relatively random or an educated guess strategy. Overall, our findings provide further insight into the working of the scale and indicate that the VAIAK has good psychometric properties and is valid as long as it is used in the intended way.