What causes this sensation?Thanks in advance.The ink in a marker comprises a dye DISSOLVED in a solvent baseWriting on a surface deposits a thin film of ink which looses its solvent through evaporation leaving behind a film of dyeThis dye will be in very fine particlesOn a relatively non-reflective surface, there will be an illusion of \'good coverage’However, on a reflective surface such as
aluminium foil, there will be significant spaces between the dye particles to allow light to be reflected giving the illusion that the ink is less prominent than on a non-reflective surfaceIf the marker pen is based an ink that uses a PIGMENT suspended in a solvent base (paint marker), the effects will be less noticeable.Other related question