to make a negative of an item, first make a glob of the plastic roughly the same size of the item.
the next step is to compress the 2 together making sure not to leave any empty space between the 2.
also for this step cut off any extra that may be push to the outside.
after that separate the glob of plastic from the item, and let cool.
and you now have a negative of what you want.
We have a be nice policy.
Please be positive and constructive.