In ceramics or pottery what is the meaning of the term, "igloss"? This
is listed in tables of the chemical composition of pottery.

What you're seeing isn't actually a single word, "igloss." It is "ig
loss," the abbreviation of "ignition loss." This is a term used in
pottery, ceramics, and porcelain manufacture. It refers to the loss
that occurs as a result of the firing process. The "ig loss" is
usually expressed as a percentage. Some loss is expected, because of
moisture and mineral impurities.

Here are a couple of typical uses, abbreviated and unabbreviated:

"Indian Feldspar
 Used for Glass, Ceramics
 Origin India
 Chemical Composition
 SiO2  68% 
 A12O3  18% 
 Fe2O3  0.04% 
 Na2O  2% 
 K2O  12% 
 Ig.Loss  0.06%"

Tokai Kogyo Co. Ltd.: Raw Material for Glass and Ceramics
http://www.tokai-kc.co.jp/english/works/works01.html

"We supply Sulphoaluminate Clinker. 
Specific Surface Area: 400-475m2/kg; 
Density: 2.8g/cm3 Min; 
CaO Free: No; 
Ignition Loss: 0.5%Max"

Worldbid International Trade Leads
http://www.worldbid.com/showrooms/showroom_homepage.htm?session=&userID=934518

I have noticed that the most common use of "ig loss" tends to be on
Asian websites. In the US and the UK, you'll more often see the terms
"LOI" and "IL":

"LOI = Loss On Ignition 
 IL = Ignition Loss 

Both terms mean that mass of the material which became volatile and
escaped the analysis. This is principally water, sulphur and carbon in
various forms, but may also include halides (Cl, Fl, Br, etc.), noble
gasses (He, Ne, Ar, etc), other non-metals (O, N), and to some degree
the more volatile metals, such as lead. Most potter's analyses are
intended to show the metals and metalloid (plus phosphorus) content,
reported as oxides of a particular degree or oxidation (e.g., iron as
Fe2O3 or FeO2). Most of the volatiles are therefore not of interest,
and the LOI or IL figure is useful simply to tell how much extra
material must be used in order to obtain the analysis quantities of
the oxides, as in preparing a recipe."

Potters: Ceramics Web Materials Database
http://www.potters.org/subject15778.htm

Google search strategy:

Google Web Search: "ig OR ignition loss" pottery OR ceramics OR porcelain
://www.google.com/search?hl=en&q=%22ig+OR+ignition+loss%22+pottery+OR+ceramics+OR+porcelain

Google Web Search: "loss on ignition" pottery OR ceramics OR porcelain
://www.google.com/search?hl=en&q=%22loss+on+ignition%22+pottery+OR+ceramics+OR+porcelain

I hope this is precisely what you need. If anything is unclear or
incomplete, please request clarification; I'll be glad to offer
further assistance before you rate my answer.

Best regards,
pinkfreud

This is precisely what I needed.