What you need6 tbs White vinegar
(4) 0.1 oz. packets unflavored gelatin
1 tbs Vanilla extract
Start by bringing the vinegar to the boil in a pan.
Add the gelatin and stir until it is dissolved.
Add the vanilla extract and stir until well mixed.
Whilst still warm brush a thin layer onto the back of an envelope flap. Set it aside and allow it to dry.
To stick the envelope moisten and press it closed.
Store unused mix in a airtight container and to re-apply the glue to envelopes warm the mixture in a pan and re-apply it to the envelopes whilst it is still warm.