Much like a rock star, "fans" of your work want to follow you. They want insider access to you.
Many art marketing coaches recommend you "bribe" people to sign up for your newsletter by offering them something free. This is another mistake that we classify under the Marketing Guru Myth. It's a mistake because it works for marketing information, of the type "marketing gurus" sell, but it actually runs slightly counter to the right way to build an upscale art brand.
People don't need to be "bribed" with a lead magnet to want insider access. Getting direct access to you through an email list is enough. There are so many ways that you can personalize your emails to give each of your readers an unique experience.
Simply invite people to join your Insiders List for Stories of Inspiration and First Access to New Work. This makes people feel like they are part of an exclusive list and furthers their personal connection to you.
You don't need a popup (click here to read more about why they don't work in the art world). You don't need an "ethical" bribe. Adding a popup or lead magnet to try and entice people to join your list is just polluting your list.
You want people who are actually going to open your emails, read them, and engage. Someone who is joining your list for the freebie is not going to engage in the future.