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I am doing some paint mixings involving quite precise proportions of paints. I am mixing my components in PP or PS (polypropylene, polystyrene) 60ml bottles, see: Bottles datasheet

Quite often, my hand attracts the bottle that sits on the precision scale, which is very annoying because it is nearly impossible to make a correct weight measurement in these conditions. The displayed weight for the empty bottle goes from zero to about -100mg when my hand goes near the top of the scale (the bottle is attracted which makes the reading negative)

Pictures of the scale in action without my hand, and with my hand:

without hand nearby

with my hand on top of the scale

See the video here: attraction

Is there any simple way to get rid of this? Any way to "discharge" the bottle (if the responsible cause is electricity as I guess it is)? What are the usual precautions to take in this case?

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    $\begingroup$ Please define uncommon acronyms on first use. Here, in the subject, $\endgroup$ – garyp Jan 26 '17 at 11:47
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Without further experiments, it's not obvious to me that electric charges are really at play. It could be air currents that are disturbed by the presence of your hand for example.

In my experience, most sensitive weight measurements cover the scale with a cover or bell jar to make precise measurements. This should work for you.

If you want to pursue the electric attraction route, you could try wearing an electrostatic discharge strap such as those worn by people who work with sensitive electronic components. You can find them quite cheaply.You may achieve the same effect by touching a grounded conductive surface before touching the scales. If the bottle is charged, then covering it with a conductive material, like aluminium foil might work, if the scale pan is grounded. You could also see if you observe the same effect with other materials.

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  • $\begingroup$ There are no air currents for sure. I see that after putting the bottles in water, the effect disappears. So I guess the hypothesis is valid. However wet bottles is problematic as it dilutes the paints. When I dry them, friction makes the problem re-appear. Any idea? $\endgroup$ – adrienlucca.wordpress.com Jan 26 '17 at 11:28
  • $\begingroup$ Also, the effect varies depending on the bottles. Sometimes it is strong, sometimes weak or absent. If I use a bottle that has just been dried with a tissue, it's the worst. $\endgroup$ – adrienlucca.wordpress.com Jan 26 '17 at 11:30
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    $\begingroup$ In my answer, I suggested using an ESD strap on yourself. You could also try grounding yourself by touching a grounded surface. Or maybe if you cover the bottle in a conductive covering like aluminium foil. If the pan of the scale is grounded, it should prevent any electric field. $\endgroup$ – Gremlin Jan 26 '17 at 11:34

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