Typically in the .info file. (you got that one) I suspect that themes have to have support for subthemes and Bartik probably doesn't so you actually have to copy the entire theme and change all occurrences of Bartik everywhere. some of the directories have the bartik in their names..

On Wed, Oct 9, 2013 at 4:02 PM, Chris Miller <cjm@tryx.org> wrote:

From: "Walt Daniels" <wdlists@gmail.com>
To: support@drupal.org
Sent: Wednesday, October 9, 2013 12:52:41 PM
Subject: Re: [support] Trivial sub-theme: Renaming Bartik

You also have to change all occurrences of Bartik in the files to your new name.
I don't think there are any such occurrences. Which "files" do you mean?
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