Re: Graffiti at WKLB. | Forum — The Modern Antiquarian

West Kennet Long Barrow 14

Image by Paul C

Graffiti at WKLB.

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LancsLass Mar 31, 2005 12:52:09

Replying to FourWinds

quote:Because chalk doesn't desolve in water and so will not wash off (even if done in a place where it's exposed to the elements). Removing it necessitates an abrasive procedure.
You talk absolute rot Mr Fourwinds chalk washes away quite easily with a little water over a short time it does not need to disolve to do this and i never said it was right just seems to be a lot of fuss over nothing!

rocknicker Mar 31, 2005 13:20:05

Replying to LancsLass

the action of actually rubbing a bit of stone over another causes some abrasion, even if it's soft.

Littlestone Mar 31, 2005 13:57:39

Replying to LancsLass

You're kinda both right (you and FW).

A lot depends on the support (the surface to which a pigment or paint is applied such as canvas, paper, silk etc ). Chalk on a blackboard is going to wash off fairly easily because the blackboard's relatively smooth. Chalk on a sarsen stone is going to be more difficult to remove because it's been deposited in the micro cavities of a much rougher surface.

Fortunately chalk has little or no binder (an oil or animal protein etc which is used to bond the pigment together to form a paint) so solvents would not generally be required.

FourWinds Mar 31, 2005 16:34:36

Replying to LancsLass

>> You talk absolute rot Mr Fourwinds chalk washes away quite easily

I didn't say it doesn't wash away did I? I might do, but may I refer you to this:

http://www.brewingtechniques.com/library/backissues/issue2.3/miller.html

"Carbonate and bicarbonate differ, however, in that bicarbonates are considerably more soluble than carbonates. <b>Calcium carbonate (chalk), for example, is only slightly soluble in neutral (pH 7) water </b>; calcium bicarbonate is considerably more soluble."

You see it doesn't desolve, but particles of it will get carried in the water. If it's on a rough rock surface then it gets stuck in the surface and can not get washed away, beacause sufficient water can't get behind it to lift it up and carry it away.

School chalk isn't actually pure chalk (or even actually chalk at all in some cases) and has bits added to it to make it disolve in water.

So, next time you say someone's talking rot make sure that they are, otherwise your amazing lack of knowledge might be noticed by a few people :-)

Graffiti at WKLB. lock

Graffiti at WKLB.