Series editors' preface - Wood Tools

carbon rinse is required (Burnstock and White,
1990; Koller, 1990). Detergents such as Triton
X-100 with a low CMC and fairly low HLB are
therefore inappropriate for use on unaged and
largely unoxidized oil paint films.
Calculating the amount of detergent needed
The manufacturer may give CMC in molar (M)
or millimolar (mmol) (1 M = 1000 mmol)
quantities, or as a weight percent (wt%). One
mole equals the molecular weight in grams
and a one molar solution contains this amount
of detergent made up to one litre of solution.
Thus if the molecular weight is 600 g, a one
molar solution will contain 600 g/litre. The
general formula used to determine required
detergent concentration in grams per litre is:
CMC as molar concentration (mole/litre) ×
molecular weight = g/litre needed to
achieve CMC
For example, the CMC for the non-ionic detergent
Triton XL 80N is 0.41mmol. With a molecular
weight of 442 the equation is:
0.00041 (CMC in moles) 442 (MW) =
0.181 grams per litre of solution
Three to five times this amount (0.362–
0.905 g/litre; rounded up 0.4–0.9 g/litre) of
Triton XL 80N, would be required to maintain
detergency in an aqueous cleaning solution. A
method for measuring small quantities of
liquids is described under section 12.1.1.
Another common way manufacturers
express CMC is as a weight percent (wt%).
This is a simple unit conversion from grams/
litre to grams/millilitre expressed as a percentage.
As calculated above, the required detergent
concentration for Triton XL 80N is
0.181 g/litre. This can be converted to wt% in
the following manner:
0.181 g/litre (1 litre/1000 millilitre) =
0.000181 g/ml
To express this term as a percentage, multiply
by 100:
0.000181 g/ml 100 = 0.0181%
This is the wt%.
Principles of cleaning 539
Weight percent CMC can be converted to
grams per litre in the following way:
(1) Divide the weight percent by 100 to
convert to grams per millilitre:
wt%
= grams/millilitre
100
(2) Divide grams/millilitre by 1/1000 to
convert to grams per litre
grams
1 (litre)
divided by =
millilitre
1000 millilitres
grams/litre
For example, to convert 0.0181 wt% CMC to
grams per litre CMC:
Step 1:
0. 0181
= 0.000181 g/ml
100
Step 2:
0.000181
= 0.181 g/litre of detergent
1/
1000
solution required to achieve
CMC
In order to maintain detergency in use, two to
five times this amount (0.362–0.905 g/litre;
rounded up 0.4–0.9 g/litre) would be required.
Choosing a detergent
It may be tempting to use proprietary products
such as household detergents for aqueous
cleaning. Many of the products marketed for
the general consumer have components that
may be detrimental to decorative surfaces.
Proprietary products often utilize anionic detergents
that require them to be buffered at an
alkaline pH, and contain additives such as
strong chelating agents, bleaches, brighteners,
perfumes, dyestuffs etc., that may interfere with
treatment objectives or damage the surface
being cleaned (Hofenk de Graaf, 1982).
The question of an ideal detergent to meet
the needs of a particular treatment should be
formulated in terms of the type of dirt to be
removed and the nature of the substrate or
coating being cleaned. The conservator must
know the implications of detergent classification
in terms of ionic charge, HLB, and CMC
in order to make an informed choice of detergent
that will achieve removal of dirt,