featuring old articles without messing up with the archive

Use Sticky Posts.

In the Post editor find the “Publish” section.
Next to “Visibility” click on edit and then check the “Stick this post to the front page” option there.
Click save and you’re done.

In the loop, you can check if a post is_sticky().

To loop them, you can use the post__in or post_not__in keys for your query with a value of get_option( 'sticky_posts' );.

There are also some Plugins in case you don’t want to dig in code.

Other options…

…would be to assign

• a special category
• a tag
• …or a custom field.

Edit:

Combine categories/tags + sticky posts.

Fetch »all get_option( 'sticky_posts' ) with a Tag of “Featured” (or inside Category “Featured”), then: ORDER BY post_last_modified_date LIMIT 10«.