I stand by what I said, correct orientation is determined by the mind. Mike Marotta's statement of "cultural context" applies only to a small segment of numismatic items, as the Celticcoins you cited. But I greatly appreciate his response.

Even the Celtic coin illustration shown has strong visual clues to correct orientation. The strong vertical side of the face on the obverse and the cross with arms of obvious horizontal andvertical orientation vividly display the intended orientation. It is the part of the brain "" the cerebellum "" which processes balance, coordination and perspective. Thus my attribution to thehuman mind.

Granted there are several types of numismatic items in which it is impossible to orientate, both of which are art medals. A class of Medallic Objects with a textural surface, say entirely composedof dots (bosses) cannot be orientated. Such textural designs have been made by the Paris Mint and are occasionally found in FIDEM exhibitions. The other would be designs of Mixed Perspective, withmultiple views with jumbled base lines.

However, since most coin designs are of lineal perspective they often have visual clues indicating correct orientation.

Anamorphic Perspective
I enjoyed reading Mike Marotta's article "Viewing Coins Obliquely". The art historical term is anamorphic perspective. I wrote a paper on this in 1976 and another in 1982 for mymaster's thesis.

One-point linear perspective was the mapping out of a grid to place objects in a picture into correct perspective toward a vanishing point which was typically placed dead center. The beauty of thepictures was enhanced when viewed standing in front of the picture. The idea was developed by Leonardo da Vinci to overcome the limitations of one point linear perspective since those paintingslooked flat when viewed from any angle.

The portrait of Ginevera de'Benci in the National Gallery of Art, Washington, D.C. Ailsa Mellon Bruce Fund, No.2326, is the earliest known portrait painted in anamorphic perspective.

The picture when viewed standing directly in front is a subtle distortion rather than the correct one-point linear perspective. Leonardo placed her face within a circle so that the distortion isso subtle that you do not realize it.

Leonardo managed this optical trick with finesse by bisecting the face in the three-quarter view on the left and the frontal perspective on the right.

However, from any angle the face is seen in perfect three-quarter view.

To read the earlier E-Sylum article, see:
VIEWING COINS OBLIQUELY (http://www.coinbooks.org/v21/esylum_v21n09a18.html)