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You will need three tables: [Shows], [Paintings], and a junction table [Entries].
The [Shows] table would have the names of the shows and other relevant information. There would be one row per show.
The [Paintings] table would have one row per painting. You can even include a picture of the painting as an attachment.
The [Entries] junction table will show the relationships between the Shows and Painting. Create a field that is a linked record to the [Shows] table and allow linking to only one record at a time. Create another field that is a linked record to the [Paintings] table and allow linking to only one record at a time. Each row will represent a unique combination of a painting entered in a show. This table will also hold the response for the painting (accepted or denied).
Is the base for your personal use or are you using it to track entries from multiple artists? If you want to track entries from multiple artists, then you will also want a table of [Artists]. How you setup that table will depend on whether each painting is by a single artists or if multiple artists can collaborate on a single painting.