The color of glass will vary in intensity from thin areas like the shoulder
of a bottle to the much thicker base.  However, the overall hue (i.e., the
color chips on one page of, say, the Munsell Book of Color) will not change
for each vessel in a specific color group, just the chroma [degree of
departure from grey] and value [lightness or darkness].  The best way to
identify the color of a large collection of glass sherds like that from Rio
Piedras is to sort it into fairly homogeneous color groups and then record
the Munsell or other color system's hue (e.g., 7.5 PB in the Munsell
system) followed by the range of chroma and value (e.g., 7.5 PB 5/8-7/10).
There is absolutely no need to sort glass fragments into tight little
groups; otherwise you may find that all the necks of one bottle type fall
into one color group while the body sherds fall into another.  For overall
color designations it is best to use the general Munsell hue names (e.g.,
purplish blue [PB] and greenish yellow [GY]).  One may add such qualifiers
as dark, light, etc. This is about all that needs to be recorded except for
diaphaneity (the degree of opacity).
 
The Munsell Book of Color, Glossy Finish Collection.Munsell Color, Macbeth
 
     Division, Killmorgen Corporation, Baltimore (1976), is the best
 
     standard for designating the colors of glass, ceramics and other
 
     materials.  Another cheaper alternative is:
 
 
PANTONE Textile Color Guide - Paper Edition.
 
     Pantone, Inc. 590 Commerce Boulevard, Carlstadt, NJ 07072-3098. 1992.
     1,701 color swatches, index. $99.00 (paper fan deck).
 
 
(The following is an excerpt from my review of this guide which appears in
 
full in BEADS vol. 7, 1995):
 
     Pantone, Inc., produces a number of color guides and selectors in
 
various formats but the one with the greatest potential for the bead
 
researcher is the  PANTONE Textile Color Guide - Paper Edition. This is in
 
the form of a paper fan deck which displays 1,701 color swatches, seven per
 
page and each with its name in six languages plus the Pantone reference
 
number. While the reference numbers are quite clear, the names are on the
 
borderline of readability. There is no introductory text to speak of
 
(unlike The PANTONE Book of Color), and the index is arranged by color
 
reference number and not the color name (as in the book). The color
 
swatches are arranged in three groups: 1) Clean and Bright Colors; 2) Muted
 
and Dull Colors; and 3) Earth Tones, Gray Tones, Off-Whites and Specialty
 
Colors. Consequently, one has to check all three sections to make sure all
 
the possibilities have been covered.
 
     How does the coverage of the Pantone color fan compare with the other
 
color charts?  A quick tally reveals that my copy of the Munsell Book of
 
Color, Glossy Finish Collection contains 1,553 enamelled plastic color
 
chips, the Color Harmony Manual contains around 947 larger chips, while the
 
Centroid Color Charts contain less than 500 swatches. Thus, with 1,701
 
swatches, the Pantone fan exceeds even the Munsell book's coverage.  At
 
one-fifth the price, the PANTONE Textile Color Guide - Paper Edition is
 
what might be termed a "best buy."  The PANTONE Book of Color is
 
recommended for its introductory text which will allow researchers to
 
better understand color concepts and how colors are perceived by different
 
cultures.
 
 
 
Happy sorting!