Natural is nice at Partisan Artisan, where pictures are worth more than a thousand words. These are posters with a point of view - incorporating a significant message with art. "Chemical Cuisine" ($3), a Nutrition Action poster in primary colors, lists food additives to avoid and those which appear safe, while stripping the mystique from such neighborhood supermarket goodies as propyl gallate, carrageenan and butylated hydroxytoluene (BHT). "Nutrition Scoreboard" ($2), a hot pink and orange grouping to nutritional value, and "Calories" ($4), an aesthetic arrangement of multi-colored still-lifes and unappetizing numbers (an average sundae is 400 calories), are more healthful enhancement for kitchen walls.This month's theme is ecology, featuring a series of unlimited edition silkscreen posters by Alexander Calder, Roy Lichtenstein and Ernst Trova ($15 to 25) which advocate "Save Our Planet" and its various components - people, fishes, wildlife, wilderness. Or, for a universal Mother's Day greeting, nothing outdoes the large (40 x 31, $3), dark photograph of Earth, with bold white letters urging, "Love Your Mother."

Partisan Artisan, 1334 Wisconsin Ave. N.W. Tuesday, Wednesday, Saturday, Sunday, 11 a.m. to 6 p.m.; Thursday andFriday, 11 a.m. to 9:30 p.m. 338-5492. -DEBRA STAR