Flame Veils (불꽃너울,Bulkkoneoul) are the aura emitted by a dragon. As such, it is regarded as a symbol of power.
Flame Veils are able to create imagination into reality, turning something into a tangible object.
Since Dragon Artifacts contain a portion of a dragon's power, these items also exude Flame Veils from their Cores, though only a slither (Third-Class Artifacts are shown not to have any). Dragon Artifacts that were directly created by a dragon are the only items that release thicker Flame Veils.
A physical difference between a limited and a named Artifact would be its display of Flame Veil, the former showing only a slither from its Core, whilst named Artifacts have thicker and more defined Flame Veils.