Cast bronze plaques are the material of choice for exterior as well as interior applications.
Although the finish of bronze will naturally patina over time, the material itself will not deteriorate.
Objects made from bronze submerged in seawater for over 3000 years have been found still in excellent condition.

The weight of a cast bronze plaque may be roughly estimated by calculating the cast bronze plaque's volume in inches (height x width x depth) by .31.
For most smaller plaques (under 36" x 30") allow 0.25" as the approximate depth. For plaques over 36" x 30", use 0.375" as the approximate depth.

EXAMPLE
For a 36" x 24" cast bronze plaque, calculate 36 x 24 x .25 = 216 cubic inches. 216 x .31 = 66.96.
Therefore the cast bronze plaque's estimated weight would be 67 pounds.

A cast aluminum plaque is approximately one-third of the weight of a comparable sized cast bronze plaque.
In the above example, simply divide the answer by 3. So a 36" x 24" cast aluminum plaque weighs approximately 23 pounds.