(iv) paradoxically, in view of (iii), a soaked-in appearance
(and despite that, the extra deposit at line-endings can be
thick enough to cast a shadow with very low-angle
illumination).
The absorbance by Frixion ink of radiation in the red and
infrared region of the spectrum varies according to the colour of
the ink. That of the green ink extends furthest into the infrared but
even so that ink is transparent at 715 nm and longer wavelengths.
All four colours were luminescent under conditions for red and
infrared luminescence [9,10].
Samples of writing in Frixion inks were viewed through
several dichroic filters [11]. Each dichroic filter was a combination
of a blue and an orange filter chosen from the range of each
supplied by Lee Filters [12]. The effect of dichroic filters in this
context is thought to depend on the colour vision of the observer.
In particular how the observer's colour vision interprets an
absence of light from part of the visual field where, for example,
an ink-line is reflecting no light that the filter will transmit, when
the remainder of that visual field is saturated with the colour,
reflected from paper, that the filter will transmit. Viewed through
each of the dichroic filters used by the author the blue Frixion ink
appeared black and the black Frixion ink appeared red. The other
two colours of ink appeared to be only slightly modified by the
filters.
Under 366 nm and 254 nm ultraviolet light all four colours of
Frixion ink simply appeared dark against the bright paper
background.
The body of each of the Frixion pens is fittedwith an eraser that
is made of a hard but conformable polymer with a slightly
textured surface. It appears from the manufacturer's advertising
that the action of the eraser is not so much to abrade the ink-line
but to generate heat through friction and decolourise the ink-line.
Writing made with each of the Frixion pens was rapidly and
completely decolourised by the heat from a domestic iron, at a
moderately hot, “two dot”, setting applied through a protecting
sheet of plain white A4 paper. The heat from a much cooler iron,
“one dot”, applied in the same way achieved the same effect.
Indeed, the heat radiating from the iron onto the writing
decolourised the inkswhen the iron was still one or two centimetres
from them. The air-stream from a low-power domestic hair-dryer
on its lowsetting decolourised an A4 page of “Frixion” writing in
1–2min. The temperature of the air-stream at the paper surface was
approximately 50 °C. The time taken to decolourise an A4 page of
writing may seem excessive but, at that temperature, applying
warm air for a short time produced only transient decolourising.
The colour of the inkwould return in one area of the page as the airstream
was moved to another.