Preheat your oven to 200 degrees Fahrenheit.
Lay the clock face flat on the center of a baking sheet.
Boil a cup of hot water and pour it into a cup. Add a teabag to the water; use a light herbal tea for mild antiquing and a strong dark tea for a look of greater depth and shadows.
Steep the tea in the water for 10 minutes, then remove the teabag from the cup.
Pour about 1/4 cup of tea slowly over the clock face. Spread the tea evenly with a foam brush.
Blot the tea from the clock face and pan using paper towels, leaving the cardstock saturated but not pooled in liquid.
Place the baking sheet in the center of the oven so the heat will dry the clock face. Watch the cardstock as it dries, looking for the point at which the edges of the material begin to rise from the baking sheet.
Remove the baking sheet and clock face from the oven once the edges rise. The tea will have discolored the clock face, giving it an antiqued look. Allow the cardstock to cool, then remove it from the baking sheet and place it onto a clean, flat surface.
Place a few large books onto the clock face overnight to flatten it out before replacing it in the clock.