Not sure what the score value you need to be silver etc, but just keep submitting your work and you will eventually gain higher medals, it works like that for all categories.

:)

Haha! That is cool!, he is probly one of my favoroute game characters if all time!

 Art aficionado (bronze): "favorite" at least 5 submissions.

 Art aficionado (silver): "favorite" at least 40 submissions.

 Art aficionado (gold): "favorite" at least 100 submissions.

 Talkative (bronze): Make at least 10 comments on submissions or in the forums.

 Talkative (bronze): Make at least 200 comments on submissions or in the forums.

 Talkative (bronze): Make at least 500 comments on submissions or in the forums.

 Popular (bronze): Receive at least 5 "favorites" on your submissions.

 Popular (silver): Receive at least 40 "favorites" on your submissions.

 Popular (gold): Receive at least 100 "favorites" on your submissions.

 2D art contributor (bronze): Submit at least 1 2D art asset.

 2D art contributor (silver): Submit at least 15 2D art asset.

 2D art contributor (gold): Submit at least 50 2D art asset.

 Music contributor (bronze): Submit at least 1 music asset.

 Music contributor (silver): Submit at least 15 music assets.

 Music contributor (gold): Submit at least 50 music assets.

 Sound contributor (bronze): Submit at least 1 sound effect asset.

 Sound contributor (silver): Submit at least 15 sound effect assets.

 Sound contributor (gold): Submit at least 50 sound effect assets.

 3D art contributor (bronze): Submit at least 1 3D asset.

 3D art contributor (silver): Submit at least 15 3D assets.

 3D art contributor (gold): Submit at least 50 3D assets.

 Texture contributor (bronze): Submit at least 1 texture asset.

 Texture contributor (silver): Submit at least 15 texture assets.

 Texture contributor (gold): Submit at least 50 texture assets.

 Document contributor (bronze): Submit at least 1 document asset.

 Document contributor (silver): Submit at least 15 document assets.

 Document contributor (gold): Submit at least 50 document assets.

 Art contributor (bronze): Submit at least 20 assets of any type.

 Art contributor (silver): Submit at least 100 assets of any type.

 Art contributor (gold): Submit at least 500 assets of any type.

Weekly challenge medals. All of the challenges and cotests listed below are closed. However, there may be new challenges in the future. A few challenges used unique medals.

 Contest participant: Participate in one of the occasional contests (or challenges?) hosted on OGA.

 Contest winner: Win one of the occasional contests (or challenges?) hosted on OGA.

 Miniboss challenge participant: Participate in the Miniboss art challenge (contest closed)

 Miniboss challenge winner: Win the Miniboss art challenge (Congratulations, Sunburn!)

 Winner 3rd place: Tempest in the Aether challenge - contest closed. Congradulations, ubunho and bart!

 Winner 2nd place: Tempest in the Aether challenge - contest closed. Congradulations, nander!

 Winner 1st place: Tempest in the Aether challenge - contest closed. Congradulations, Kieve!

Other medals. 

 Contest judge: Help judge the occasional contests (or challenges?) hosted by OGA. Not sure what the application process is to become a judge.

 OGA supporter: Pledge at least $10 on Patreon for OpenGameArt.org's continued awesomeness.

 Site administrator: Volunteer to become a site administrator on OGA. PM one of the senior Admins, like Bart, Redshrike, p0ss(?), Botanic, Sharm, or Clint Bellanger. Of course, they are under no obligation to promote anyone to admin status. Some form of interview may follow. 

 Founder: Steal bart's identity. Seamlessly integrate yourself into his daily life. Take over his responsibilities. Let no one know of your deception.

I think that's all of them. Did I miss any?

Sure! :) 

It is probably obvious that many of these medals are easily obdained via abuse. Commenting on every topic and submission with "Hi", "Hi", "hi" just to get the Talkative medal, or submitting a collection of artwork one tiny peice at a time in order to spread the submission count, etc. I would hope people don't do that kind of thing. For the most part, though, everyone seems to enjoy the medals and earn them for the honor they convey. :)

interesting...

Medals and achievements are essential to keep people connected to your project.