coming to terms with gum

FWIW, below are definitions for terms as I use them in reference to gum
printing. Hopefully this will help eliminate any confusion for someone
reading my posts on the matter of gum printing. I've also made a couple
suggestions for using specific terms when referring to this or that.
Hopefully these suggestions make sense.

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Density: not a very useful term in itself since it can refer to optical
transmissive density, reflective density, mass/unit volume, and
decreased mental capacity of gum workers suffering from long-term
exposure to various chemicals and life.   :)
Transmissive Density: optical density as measured with a transmission
densitometer.  The transmissive density is the log of opacity.  While
this term is useful in silver printing or when measuring the opacity of
the light attenuator, it probably has little practical value in gum
printing other than identifying the value of optical transmission of the
step wedge or the negative being used for printing.  Since we generally
print on a paper substrate and not glass or some other transparent
medium, referring to the "density" of a gum print is not referring to
the opacity/transmission of the printed image.  In my opinion, the term
should only be used to in reference to the negative or stepwedge, and
not the print.
Reflective Density: a logarithmic measure of the reflectance of a
surface.  This measure might have some utility in gum printing except
for the fact that no gum printers I know of use a reflection
densitometer when printing.  I believe this term is being confused with
"tone", "print value", "step", etc., in the current onlist discussion. 
IMO, should not be used except when stating relative observations
regarding printed maximum and minimum densities which are readily
observable even though their actual reflectance may not be known.
Transparency & Opacity:  Confusing in reference to gum printing.  Some
pigments are opaque (e.g., titanium white), yet high in value.  Others
are dark and opaque (e.g., lampblack).  Then there are transparent
pigments (e.g., phthalocyanine blue).  IMO, for gum printing, we should
restrict the terms opacity and transparency to the relative appearance
of pigments in terms of how well the colors block underlying
layers/colors or when discussing the specific optical density of the
light attenuator.  And, we should be careful to specify in which context
we are using the terms.
Tone:  The relative value (light vs. dark) of the image deposit which is
visually observed in the print or the appearance of a pigment in terms
of relative reflective value.  For example, light tones vs. dark tones,
light vs. dark pigments.
Exposure Scale (ES):  in absolute terms I take this to be the
transmissive density difference between the maximum and minimum density
values  printed using a transmission density step wedge which result in
distinct print values and are not blocked compared to both adjacent
tones.  For example, if the stepwedge is printed so that only steps 3
(transmission density = 0.35) through step 15 (transmission density =
2.15) are distinct, the exposure scale would be the inclusive difference
between steps 15 and 3 resulting in a relative 12-step exposure scale
having a specific density range of 1.80 density units.
Negative Density Range (DR):  the total range of key transmissive
densities of a negative from most to least dense.  ("Key  transmissive
densities" meaning here the negative densities associated with desired
textures and tones of the subject which are to be reproduced as specific
visualized values reproduced in the print.)  This term is often confused
with exposure scale.  However, they are not the same thing.  To optimize
printing, the density range present in the negative should be matched to
the exposure scale of the print medium.  Negative densities which fall
outside the range of the print exposure scale will not be reproduced
without further manipulation of the printing process (burning-in,
dodging, print overexposure, curve manipulation, long or short soak,
etc.).  Additionally, depending on who you read, the optimum density
range of the negative to match a specific print process may be reported
with wide variation.  (Some authors take the negative density range to
be from maximum to minimum tones, others from zone II to zone VII,
others from zone III to zone VII, and still others from 0.10 above fb-f
density to some highlight negative density, etc.)
Thickness of reaction product:  Is anyone actually measuring this?  I
take it to refer to the physical relief of the gum image, pigmented or
not.  Doesn't make much practical sense to talk about it, IMO.
Dichromate "Image":  The physical deposit of reacted dichromate present
in a gum print, pigmented or otherwise.  The dichromate image is usually
tan or light green and has printed out beneath the light attenuator in
response to exposure.
Dichromate "Fog":  A term I use to refer to random deposit of tan or
green reacted dichromate akin to the familiar term used in silver
printing.  Heat fog, chemical fog, random exposure fog, veiling, etc.,
in gum printing are non-image reacted dichromate.  I believe some gum
printers refer to this deposit as "dichromate stain" which IMO is
confusing and innaccurrate.
Dichromate "Stain":  Another confusing term which I take to refer to the
yellow-red dichromate chemical which might remain in a gum print given
extremely brief washing.  I've never observed this type of staining in a
fully processed print.
Gum Image:  the printed image resulting from trapping pigment in an
exposed and fully processed gum print.
Pigment Concentration:  How much pigment is in the gum bichromate
emulsion.  Ideally it would be expressed in grams per solution volume. 
An example would be 1 gm pigment in a combined 10 ml 14B gum arabic +5
ml saturated potassium dichromate solution.  However, other units of
measurement are frequently used (e.g., an inch of pigment, a pea-sized
drop, etc.,) although not with the same degree of accuracy implied by a
mass/volume measurement (i.e., "density" in the strict sense of the
term).
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Joe