Directors wishing to portray a definitive era in a movie use certain techniques which also produce nostalgic emotions of a sense of authenticity which are both beneficial to cinema as art and a commercial product. In Films such as O’ Brother, Where Art Thou? (2000) the colour brown is used to produce an affect of a faded and lost past. This makes the film similar to looking at a very old photograph aged sepia-brown. This imbues the whole form of the film with a sense of a by-gone era. The use of browns also strips away, or inhibits, the editors’ [or whoever] ability to produce a slick glossy product as sepia-brown ensures an aesthetic affect which communicates a reality opposed to the whole editing process.
Another common technique, used more and more regularly due to the financial importance of a film having a commercially viable soundtrack, is the use of music. This is normally non-diegetic however occasionally this is a main part of the diegesis. One movie that uses music to produce a sense of era is Donnie Darko (2001). All through the film a classic eighties soundtrack is played which injects a sense of place, time and atmosphere. Using music of a definitive era helps communicate the atmosphere that the director wants as they can use a specific genre of music to imbue the film with an emotion. The music of the seventies can both be used to communicate a riotous sense of anger with a punk soundtrack and create a sense of love and romance with a use of disco soundtrack.
The Motley View 
