In this case, expertise means having the knowledge necessary to determine the origin and age of an instrument or bow.
It goes without saying that the amount of ready knowledge available to an expert determines both the speed and the quality of his judgment.
Determining the origin of an instrument is still primarily done according to a “style-critical” method.
This means that the expert makes an assessment based on the model, details, paint, materials and techniques used.
Some instruments or bows can be recognized at a glance as the work of a builder or a “school”, but intelligent copies, restorations and replacement of lost parts, or even forgeries, sometimes make it difficult for us to “understand” an instrument and make a correct judgment.
In addition to our own knowledge, (photographic) memory and database, many other means are available to us in this modern time, such as U.V.-light (quartz lamp) and ancient research on the basis of the annual rings of the coniferous wood of the top (dendrochronology).
The limitation of all these new techniques is that they can help tell us what an instrument cannot be; there is no trick that tells us what the origin of an instrument is.
In addition, digital photography in combination with email makes it increasingly easier to consult fellow experts and the many good publications and exhibitions worldwide also help to practice this perhaps most difficult aspect of our profession at a high level.
Contrary to popular belief, the sound of an instrument is only of secondary importance in determining its value. The always very subjective approach to the concept of sound (for the musician the most important aspect in the assessment of an instrument) does not allow an objective determination of its value on the basis of this.