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[Patrick]

When reading some formula's they explain to do the following (or similar) "dampen it using only 8% water. I like to add 5% alcohol to the water".

Dampening with 8% water .. 8% of the composition weight? ie - 100g of comp - 8g of water? BUT, then it would be described as 8 parts of water ...

Then adding 5% alcohol to the water, that would be volume.

Thanks,

Patrick


The above came from passfire under the 4" comet.

[alany]

In pyro the solvent quantity is usually specified as a mass ratio of the total mass of composition *excluding the solvent*, e.g. +X%. However many people assume the solvent density is 1.0 and measure by volume for expediency. For common ethanol solution concentrations used in pyro the error isn't anything to worry about.

As far as the concentration of the moistening solution goes there are three common ways of specifying solution concentrations:

% w/w - mass of solute / mass of solution.
% w/v - mass of solute / volume of solution.
% v/v - volume of solute / volume of solution.

The v/v measure is usually used for liquid/liquid solutions, and w/w for solid/liquid solutions. (w/v isn't used much, but molarity is basically done w/v.) So ideally alcohol solutions are v/v and NC lacquer w/w, however it should really be specified which you mean. The w/w system is nice because it is easily converted to "parts per X" just by multiplying and it doesn't change with temperature or pressure.

I typically just "moisten to feel" and not measure my solvent accurately, especially for compositions I am experenced with. Keeping a bit of dry composition on the side can help fix up over-moistening accidents, as can running the composition through a sieve a few times and spreading it out to dry for a while.

BTW, parts don't need to be percentages, they are just ratios of mass. Many people normalise the parts into a percentage, not really sure why, it isn't all that helpful IMO, it is just more base-10 dogma.