Re: Standard formula

On Wed, 26 Dec 2001, Patrick Clark wrote:

> 1) be consistent in your terms or at least give examples that illustrate
> your idea how terms should be used. For example: 10% gel (100g per 1000ml
> of water) or 25% sugar (25g sugar for 100g gel)

Yes Yes Yes ... strongly agree!

> 2) The most confusing item I have run into is pigment concentrations.
> Sandy in your carbon primer you suggest 40 g of sumi ink. In your tables
> regarding various concentrations of dichromate you state 40ml sumi ink. I
> thought that 40 ml sounded more likely and mixed my first batch using 40 ml.
> Now, after reading these latest posts Im back wondering which is correct.

I should probably let Sandy answer this, but since I've already started
typing ...

The original metric system definition of a gram was the mass of one cubic
centimeter of water at standard temperature and pressure. A cubic
centimeter is also the definition of the milliliter. So ... 1 ml of water
should be very close to 1 gram.

It isn't uncommon to see people using these measurements interchangeably
for aqueous solutions. In general it is probably a reasonable
approximation, but you should be aware that it is just that - an
approximation. For carbon printing purposes it is probably good enough.

(An interesting bit of trivia is that the liter is not an official unit of
the new SI metric system.
<http://physics.nist.gov/cuu/Units/outside.html>)

> 3) Back to the pigment issue. Some times you guys ( lovingly said) refer
> to lamp black and carbon as the same thing.

Carbon is the name of the element. The term lamp black comes from the
method of obtaining a concentration of the element. In this case, lamp
black refers to the old method of collecting the soot from an oil
lamp. Other terms are:

    charcoal - carbon obtained by destructive
                                distillation of wood products

    bone black or Ivory Black - carbon obtained by destructive
                                distillation of bone material.

The impurities and the size and shape of the pigment particles produced
by each of these methods tend to give certain shading to the type of
black. Lamp black tends to be a more bluish black than the browner tones
of Ivory black, etc..

> 4) Also pigment thing. Are you using dry pigments or watercolor pigments
> from a tube when weighing in grams. I realize I maybe being very dense
> here.

Both - some people swear by dry pigments, others by watercolor
pigments. Watercolor pigments tend I think to be simpler since they are
already in a suspension. Dry pigment can be a bit tricky to mix since it
tends to float on the surface of the water. Either works though, and
measuring both in grams is probably the "best" method. One should specify
what type of pigment is being used and very possibly the brand name too.

- Wayde
  (wallen@lug.boulder.co.us)

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Received on Wed Dec 26 14:40:06 2001