When artwork is made by the artist and assistant, is it less valuable?Should artwork be made by one person only; should the assistant get credit?

Many contemporary artists, chief among them Damian Hirst,
use assistants to create their work. In terms of the value of his work, the use of
assistants has not diminished it. In fact, the diamond-encrusted skull which Hirst
conceptualized (but did not make) sold for its asking price of 50 million British
pounds.

Some of Hirsts' assistants are named and artists in
their own right. They do get some credit but are not generally discussed and are never
put in the same category as their boss.

A quote from an
article discussing Hirst says:

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"Fifty million pounds might seem like a
ridiculous amount of money for diamonds arranged on a platinum skull, but it's all about
the uniqueness of the idea and the fact that there will always be only one piece like
it. Mark my words, it will be
sold."

Hirst is not the first
to employ these methods--the great masters of old used many assistants to create their
famous paintings. The value of those works remains extremely high, and it is not
considered a 'black mark' that assistants were used.