Recently I stumbled upon several projects my daughter completed as an Explorer. To complete the Home Decorating Merit Badge, she created a set of interchangeable Seasonal centerpieces. 
SUPPLIES:
1 batch air dry clay (here)
Rolling pin
Seasonal cookie cutters
Acrylic craft paint and brushes
Bamboo skewers
Hot glue gun
Mason jar (or other decorative container)
Glass marbles or rocks
She began by making one batch of air dry clay (recipe found here). After rolling the clay into a sheet, she cut a variety of different shapes. After the clay was completely dry, each piece got a coat, or two, of paint.
When the paint was dry, I helped her to glue bamboo skewers onto the back of each piece. She was then able to arrange them in a mason jar full of glass marbles.
The centerpieces were a great addition to the patio table in our lanai.
Here is a list of other resources related to the Home Decorating Merit Badge:
NOTE: The requirements have been simplified here. Please be sure to read the full text in the American Heritage Girl Handbook to make sure you fully understand the requirements.
