I don't know about art either, I agree the wish to make the thieves looks "different" from Christ may have been sufficient reason.
Distinguishing them in that way seems have only become a common practice in the renaissance,
when there was greater emphasis on 'mimetic' realism, yet still the need to maintain a 'hierarchic' composition -
here's an example (Veronese):
View attachment 197542
Incidentally (a bit more on eul's home ground) the name Dysmas
comes from the apocryphal Gospel of Nicodemus, probably of the 4th century,
bringing together traditions that had developed around the crucifixion accounts
in the canonical Gospels. In some versions, the bad thief is called Gestas.
There is some fascinating academic writing on this subject of the treatment of the thieves in art compared to the depiction of the Christ figure (as well as the use of imagery of punishment and torture in early modern art).
Look at:
http://press.uchicago.edu/ucp/books/book/chicago/T/bo3621816.html
Here are a couple of brief, informative reviews from the Amazon site:
From Library Journal
Pain and suffering are popular motifs in Western art. Indeed, the predominant Christian theme in medieval art is the Crucifixion of Christ. To understand better this ritualization of pain and death, Merback (art history, DePauw Univ.) attempts a serious study of the Crucifixion, the execution of the two thieves, torture, and the spectacle and ritual of punishment in medieval art. While the subject matter is gruesome and distasteful, this highly specialized study does bring to light symbolic meanings of the medieval depiction of pain and punishment, and Merback does a good job of explaining pain in the context of medieval life and philosophy. In the end, however, he's trying to do too much. Despite his efforts to tie together all the historical, theological, and social elements, the text ultimately meanders. Only for specialized academic collections.AKaren Ellis, Baldwin Boettcher Lib., Humble, TX
Copyright 1999 Reed Business Information, Inc.
'This is a rich and learned book - whose lively contemplations make well-known images of the past pulsate vibrantly, as they must have done for some who viewed them half a millennium ago.' - TLS 'This powerful and well-illustrated work probes the relationship between images of the Crucifixion and the understanding of pain, suffering and justice - fascinating.' - History Today 'Merback's analysis is intelligent, stylishly written, and - theoretically informed - this imaginative study contain chunks of extremely insightful analysis, which in combination with its sheer readability, makes it the best account of medieval penalty to come out in a very long time.' - Art History 'a well produced volume with excellent use of images, both black and white and colour, to embellish the text, but a reader will need a strong stomach to attempt to digest the material it contains. This is a horrific book, as it is intended to be.' - Art Newspaper 'This is a shocking and absorbing book, strikingly illustrated - Not for the squeamish.' - Good Book Guide 'Merback's scholarship ranges widely, and with ease.' - Church Times
--This text refers to an out of print or unavailable edition of this title.
Another fascinating read, studying the depiction of, in particular, female punishment and torture scenes (usually of saints) and the meaning of these images in Medieval art is:
http://press.uchicago.edu/ucp/books/book/distributed/S/bo3621696.html
Both are books that should be on the "required reading list" of most of the regular visitors to this site! (and I have no idea what is causing the line through the text I have typed!!!)
