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Recently some practitioners have
advocated the use of mixing local anesthetics with pigment.
There are a variety of phenomena in which the
color of a substance is altered by a change in the environment.
One example is "photochromism" where exposure to light
produces the change of color. With a change of temperature there
is "thermochromism"; with pressure, "piezochromism";
with acidity "halochromism"; and with electricity,
"electrochromism". These phenomena may
be reversible or irreversible, and a number of them have important
uses. (The Physics and Chemistry of Color by Kurt Nassau 1983 page
347.)
Halochromism, the change in color with the acidity
or pH is used in acid-base indicators such as phenolphthalein of
Structure (6-31) and (6-32) of Chapter 6, where a color-causing
conjugated system is formed or destroyed." (page 348)
Most colors "live" at a certain pH.
And adding an acid local anesthetic solution (pH 3.45 approximately)
would most certainly alter the chemical environment of the pigments
or dyes .
One can easily find information on the pH of both
natural and synthetic
iron oxides. Pigment Product Data Sheets breakdown pigments into
Chemical
Composition and Physical Properties. Here are the pH's of four pigments,
including 3 iron oxides and 1 titanium dioxide pigment:
1) Titanium Dioxide pH 6.5-7.5
2) Natural Red Iron Oxide pH 8.5
3) Natural Red Iron Oxide pH 6.5-8.0
4) Synthetic Yellow Iron Oxide pH 5
There is an association of Textile Chemists and
Colorists (AATCC) and the
chemistry of colorants is important. Adding acids to the above pigments
will take them out of the pH where their color exists in the natural
state.
Adding local anesthetics at an acid pH to pigments
at a normal to alkaline
pH may not make "color" sense, or common sense either.
Whether is this pH effect is reversible
or irreversible is not something to be determined by amateurs. Further
scientific study is needed to resolve this important concern.
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