These photos and descriptions will help you guage the dates of production of your Fire-King mugs.  The dates are all approximate.  Much information about the dating of Anchor Hocking’s markings can be found in Anchor Hocking’s Fire-King Glassware by Garry & Dale Kilgo and Jerry and Gail Wilkins, published in 1997.  As a general rule, the less embossing on the bottom of a mug, the older it is – however one common exception is that “Fire-King Glass” is older than “Fire-King Ware” (one alphabetic character difference!)  Also, though not specified in any of the descriptions below, the mugs made after about 1950 will usually have a 2-digit mold number embossed on bottom as well.  These mold numbers carry virtually no collector value or meaning.

NEW DATE INFORMATION!
Apparently the Company having newly formed the ribbed bottom stacking mug in the latter 1970s didn’t want to change their molds to eliminate the Fire-King embossed logo.  It is speculation on my part but that might explain why these mugs have the Fire-King script embossed on them much later than 1976 – and up into 1981, while most other mugs lost that embossing about 1976-1977 or so.

click on any mug for a larger view.

Oven Fire-King Glass  from the mid 1940s

FIRE-KING OVEN GLASS    This in block letters is visible from the inside of a rare yellow philbe mug.  It reads backwards looking at it on the bottom.  This will be from the earlier 1940s.  This backwards stamping is not an anomaly, it is seen very commonly on pie plates of this period.

OVEN Fire-King WARE    Common on the older shaving mugs and some Philbe Wannabes.  Dates to the latter 1940s.

OVEN Fire-King WARE MADE IN U.S.A.   Introduced the “Made In U.S.A.” about 1951, and this mark was used through the 1950s era.

ANCHOR HOCKING Fire-King WARE MADE IN U.S.A.  Throughout the 1960s.

ANCHOR HOCKING Fire-King  MADE IN U.S.A.  This one used on the footed mugs, missing “WARE” probably dates into the earlier 1970s.

ANCHOR HOCKING Fire-King OVEN-PROOF  MADE IN U.S.A.  This one was used through the 1970s.

ANCHOR HOCKING Fire-King OVEN-PROOF  MADE IN U.S.A.  This one is similar to above but adds morse code type dots and/or dashes and the little “wings” that come in from the heat ring.  The morse code dots, dashes and wings date to the late 1970s and as late as 1981 or so.

ANCHOR HOCKING  910 (the piece number) Fire-King (not in script) 350 (the pattern number?)  MADE IN U.S.A.   This is one of the bottom stamps for one of the institutional mugs, and could be ordered by each piece rather than in sets.

ANCHOR HOCKING OVEN-PROOF placesetters collection MADE IN U.S.A.  This is the bottom of a Vienna Lace cup or mug and dates to the early to mid 1970s.  A Fire-King era series that is not marked Fire-King on bottom.

{mold number}   This is the bottom of a 1960s era D-Handle mug showing only a mold number.  I have seen this pattern mug on Ebay, and that mug’s standard bottom stamping dated it to the 1960s.  This is also the same bottom stamp style as the B.C. series “Grog” high relief molded mug.  Genuine unmarked Fire-King mugs are a bit of a rarity (except the Grog mug where this type marking is standard).

OVEN-PROOF {mold number} {anchor inside a rounded corner rectangle} {sometimes a pattern number} and MADE IN U.S.A and possibly morse code dots and/or dashes and the “wings” that intrude into the center.  WARNING!!  This is not a Fire-King mug bottom.  This is from the post-1980 period when the Fire-King embossing stopped being used.  I consider this to be just an Anchor Hocking mug.

The Kilgo-Wilkins book lists a few other bottom stamps, such as FIRE-KING   dating from 1942-1945 
( I have never seen this one);

ANCHOR HOCKING-OVEN-Fire-King-DINNERWARE-MADE IN U.S.A., dating from the late 1960s to the early 1970s; and

ANCHOR HOCKING-OVEN-Fire-King-Suburbia-OVEN-PROOF-MADE IN U.S.A., dating from the late 1970s.