In terms of fashion, brick chimneys and mantels are often the worst offenders when it comes to looking outdated. Bare, "natural finish" brick and heavy wooden mantels can weigh down otherwise careful room renovation plans, throwing the room's design balance out of whack. Fortunately, they're some of the easiest elements to change.
Brick fireplace facings can accumulate staining over time, whether it be from past issues with adequate chimney draft or the occasional downdraft forcing smoke and ash into the room. If your decor all but warrants the brick to remain unaltered, there are products available to bring the fascia back to its original appearance. Light smoke deposits can be removed with a special hearth cleaning compound. This compound is usually only available through specialty hearth retailers. The low acid content in the sprayable compound gently eats away at deposits and allows you to blot the residual away with a damp cloth, bringing the appearance of the brick back to a clean and newly laid look. For heavy buildup of soot or smoke stains, a more abrasive cleaning compound may be needed. Muriatic acid works well for removing heavy build up, but great care must be taken when using it. Gloves and eye protection must be worn at all times. Another option is a paintable soot removal product that can be applied to the brick, allowed to dry, and then peeled off. When peeled away from the brick surface, soot stains will be lifted away as well. This option only works well on brick that is not porous.
If the desire is to shift the look of your hearth to a more modern appearance, applying a brick glaze or paint to the surface is a great way to update to a clean look. There are numerous paints and glazes on the market that meet the 300 degree temperature recommendation for the brick surrounding the fireplace opening. Before paint can be applied, the brick should be thoroughly cleaned by one of the methods previously mentioned above.
