How To Make a Collecting Tray

 1) Get a bottle with a screw cap.
Preferably the bottle should be like a hip-flask shape (flattish), smooth with no ridges/bumps.

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2) Mark out a square/rectangle as big as you can on one of the flat sides.
Leave a little margin towards the cap end.

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3) Cut the square out and clean any rough/sharp edges. Optional, leave a little lip to help stop spilling contents.

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4)  Add glue (superglue/pva) to the object in places where you want the texture to stick.

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5) Place object (base) in the tray (careful not to get glue in the tray itself).
Then sprinkle your texture (salt/sand). Pat down if need be and wait a moment. 

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6) Dig out your object and tap/brush/shake off any excess texture and then place to one side.

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7) Remove tray's cap and pour contents back into its original container.
 
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8) Replace both caps (Tray and the container for the sand).

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Now you can base your figures easily and collect all the bits!

Hope it helps!

-Dusty