'The Forge' is a sonnet with a clear division into an octave (the first eight lines) and a sestet (the final six lines). While the octave, apart from its initial reference to the narrator, focuses solely on the inanimate objects and occurrences inside and outside the forge, the sestet describes the blacksmith himself, and what he does.
Interestingly, the transition from the octave to the sestet is a run-on or enjambment containing one of the key metaphors of the poem, the anvil as altar:
Set there immovable: an altar
Where he expends himself in shape and music.
One effect of this is to enable us to experience the anvil or altar as a magical point of transition between the material and immovable world of objects and the fluid, musical world of human consciousness.
The rhyme scheme of the sonnet is: abba cddc efgfef, a departure from the standard Shakespearean (abab cdcd efef gg) or Petrarchan (abba abba cde cde) sonnet form. The unrhymed 11th line He leans out on the jam, recalls a clatter is perhaps the most striking feature of the rhyme scheme, and, combined with the poem's second run-on, serves to emphasise the cacophony and disorder of the remembered horse-drawn carriages. The threefold full rhyme nose/rows/bellows gives a pleasing finality to the end of the poem, especially in contrast to other lines which tend more to half-rhyme (square/altar, dark/sparks).
The metre of the poem is the standard iambic pentameter, but it is used flexibly, to good effect. For example in the very first line the first two feet begin with a long syllable (thus trochaic or dactylic rather than iambic), which has the effect of emphasising the important phrase All I know which frames the poem by suggesting the limits of the narrator's perspective and knowledge (the narrator seems to be outside the forge: he sees the objects outside, and hears the sounds inside, but cannot see the anvil, and only sees the...