New brick lacks the appeal and character of aged brick, the softer, blurry, variegated shades and worn edges that hint of history. Inside or outside your home, trim or a wall of brick may be aged with stains, whitewash or paint that is interesting enough that you won't want to cover it with artwork or hide it with landscaping.
Interior brick that is too new and shiny looking can be "dusted" with a film of fade with dilute white paint. Whitewash, unevenly applied, will take down that vivid color, giving bricks the look of old pinkish clay that's faded in the sun. Brick is porous, so the watered-down, water-based paint will soak into the surface, coloring it paler and duller. Experiment to find the dilute mix that delivers the degree of white overlay you want -- start with 1 part white paint to 2 parts water on an inconspicuous area and just wipe it off if the paint is too thick. Pictures of dusty old brick provide useful guides to whitewashing a wall unevenly so it looks natural.
The brick wall around the hearth gets a layer of soot and grime that darkens brick over time. You can paint that on with careful sponging and a few photos of unrestored historic hearths for inspiration. Focus on blackened brick over the firebox where smoke would have risen and settled. Use a variety of colors on individual bricks -- from true black to grays. Add some light white sponging far from the hearth opening to simulate efflorescence; moisture would have forced salts out of the brick. Keep to flat paints because soot has no gleam to it. Applying sloppy new grouting around the individual bricks also makes the wall look old, with some eroded bricks, patchily repaired many times.
A brick wall in a loft gets a theatrical historic treatment with the addition of a painted-on "penumbra" that mimics the shadows of old advertisements on the sides of brick buildings in urban industrial areas. After you whitewash or faux-age a brick interior wall, sketch or project an old billboard ad on it. You can find those on the Web and copy them to a clear projector sheet to size up for the space you want to fill, or copy one on grid paper and transfer to a mocked-up taped or penciled grid on the wall. Classic product logos and labels look authentic in a kitchen. Sports or automotive gear might work well on a den or playroom wall. Paint in the letters and icons with flat black or colored paint and lightly sand the artwork once it is dry, so it looks weather-worn. The more ghostly it appears, the better.
The historic district you live in, the neighborhood where your house is located, or the aged brick look that appeals to you will determine how you faux-age exterior brick on trim or the siding of your home. The best way to change brick appearance and color is with concrete stain. Water-based concrete stain comes in transparent colors you can dilute as well as combined stain and sealers. Check any local regulations that cover what you may do to the exterior before tackling the job. Colors may be tinted to customize the stain for the exact shade you need. The stain works on the cement grout as well as brick, so you may need to apply it to individual bricks to avoid a uniform color on the wall.