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following
> > lightbox (a sheet of well-lit white paper will do):

Bill wrote:
> A caution if trying this at home. If using a "well-lit" sheet of white
> paper
> (front instead of back lighted) and laying the filter on the paper, the
> density/color shift of a normal filter will double.  Light has to pass
> through the filter to reach the paper, then the light reaching the paper
> is
> reflected by the paper--back through the filter--to reach the observer.
> How
> might this work with a polarizing filter? I am fearful of hazarding a
> guess.

I wouldn't want to make too much of this. The white paper was only
introduced for the benefit of most of us who have no access to a lightbox.
The filters need to be held above the paper so that the filter densities/
colours can be compared. Polarizing sunglasses can be used, as far as I
know, for these polarizing experiments.

   

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