How much of a deduction can I take for the art I donated? It depends.
The people who buy the art are entitled to deduct the fair market value of the art, but the people who create the art are only entitled to deduct the costs of the materials that went into the work. However, artists (and writers and photographers) deduct the cost of all their supplies in the year they incur them. Thus the net effect of this is that the contribution that can be deducted by an artist for the gift of a work of art is actually zero.
Artists used to be able to deduct the value of their art that they donate, but the IRS doesn’t allow it anymore. Around the time of Richard Nixon, Congress changed the rules so that people who created the work could only take the cost of materials (which can be fairly meaningless). There have been bills in Congress to change this rule back but as of now they have not been passed.
As an example, a person who pays $1,000 for a work of art that becomes worth $500,000 can possibly then take $500,000 worth of deductions if they give it to an art museum who will accept it. If the artist who created this work were to contribute it, she or he would get no deduction.