Remove the punched-out circle of clay from underneath the cap and ensure your ornament fits snugly around the cap (I did this by actually laying my design over the cap and using a drinking straw to gently roll down the edges).
Now use a drinking straw again to punch a hole in your ornament for the string to be tied through.
Set your ornaments aside to dry WITH THE SAMPLE VIAL CAP NESTLED INSIDE IT.This is an important step. Your clay will shrink as it dries and close firmly around the cap. If you let your ornament dry and try to add the cap later, it will not fit.
Once dry, clean up any clay residue on the sample vial cap with a damp cloth. If the cap is still loose, secure it to the ornament with craft glue.
Thread some hessian twine through the hole in your essential oil diffuser ornament.