Fill the bag about halfway with sweets or crumpled black tissue to give it shape and weight. The bag should stand without flopping.

Write or print your potion label on white card. Border it with a fine black marker frame, add a skull or star doodle in one corner and write the potion name in the centre in your best apothecary lettering. Aged, slightly uneven lettering looks more convincing than neat print.

Attach the label to the front of the bag with a glue stick or peel-and-stick label backing. Centre it on the lower two-thirds of the bag front.

Crumple the black tissue paper into a rough ball and push it into the opening of the bag so the edges fluff outward above the bag top: this becomes the cork or wax seal. Leave about 5 cm of tissue visible above the opening.

Wrap a length of baker's twine or a strip of orange washi tape around the bag just below the tissue, at the bag neck, and tie or press it to secure. This creates the illusion of a bottleneck separating the body of the bag from the stopper.

Set the bag upright among similar bags on a shelf. The varying label names are what make the display entertaining.