self-removing marker

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When I cut out my new briefs, I used air-erasable marker liberally to
sorta-semi line up the grain of a tube that had been slashed open none
too straight.

On Monday, one of the new pairs turned up in the wash.  As is my
habit, I poured a little water on the area that gets dingy and rubbed
it with a sliver of soap.

As expected, the blue wash-out marks I'd used to match up the pieces
disappeared when they got wet.  I was surprised that purple marks
appeared when I rubbed with soap.

After a bit I remembered that the ink in a fading marker is an
indicator:  purple when alkaline, invisible when neutral or acidic.
It's alkaline when in the pen, and is slowly neutralized by carbon
dioxide, which is also known as carbonic acid.  Which explains why I
had about half a second to cut when I used it to mark cheap corrugated
cardboard, back in the twentieth century.

Soap -- I was using real soap -- is very alkaline.  And rubbing did
not make the marks disappear.  Going through the washing machine did.
Whether washing removed the mark, or merely removed the soap, I'll
find out next wash day.

I've always known that one should not use self-removing marker on a
project that will never be washed, but now I have proof rather than

joy beeson at comcast dot net
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