"Goibniu who was not impotent in smelting," - Lebor Gabala Erenn
Goibniu, or Goibhniu is the Irish God of smithcraft equated to the Welsh Gafannon. His name is derived from the word for smith; Old Irish gobha, Modern Irish gabha (O hOgain, 2006). It is said that he could forge a weapon with only three blows from his hammer (Berresford Ellis, 1987). Goibniu has two brothers, Credne the wright and Luchtne (or Luchtar) the carpenter, forming a trinity of crafting Gods. The three often work together to forge the weapons of the Gods, with each one making a part of the whole. According to the Lebor Gabala Erenn (LGE) Dian Cecht was also his brother and they were all sons of Esarg: "Goibniu and Creidne and Dian Cecht and Luichtne, the four sons of Esarg" (Macalister, 1941). Indeed the four are mentioned together at several points in the LGE such as: "In his [Nuada's] company were the craftsmen, Goibniu the smith and Creidne the wright and Luichne the carpenter and Dian Cecht the leech." (Macalister, 1941).
Goibniu was the preeminent smith of the Tuatha De Danann who made weapons in particular. Before the battle of Maige Tuired Goibniu is asked what he will contribute.
"And he [Lugh] asked his smith, even Goibniu, what power he wielded for them?
‘Not hard to say’, quoth he. ‘Though the men of Erin bide in the battle to the end of seven years, for every spear that parts from its shaft, or sword that shall break therein, I will provide a new weapon in its place. No spearpoint which my hand shall forge’, saith he, ‘shall make a missing cast. No skin which it pierces shall taste life afterwards. That has not been done by Dolb the smith of the Fomorians. I am now [gap: meaning of text unclear/extent: one word] for the battle of Magh Tuired’." (Stokes, 1926)
During the battle against the Fomorians he made peerless spears that never missed and killed whoever they hit, excluding only himself. We learn the latter fact after Brighid's son by Bres, Ruadan, goes to the forge, takes one of Goibniu's spears and wounds him with it, only to have the smith turn around and kill the would be assassin with the same spear. Goibniu is taken to Dian Cecht's healing well and recovers.
Goibniu had a special drink, a mead or ale called the fled Goibnenn, that conveyed the gift of youth and immortality to the Tuatha De Danann (O hOgain, 2006). This drink is sometimes called the feast of Goibniu and is said in some sources to cure disease (Monaghan, 2004). He also owned a cow who gave endless milk (O hOgain, 2006).
He also has some association with healing according to the St. Gall Incantation in which he is invoked to remove a thorn, possible also a reference to healing a battle wound:
"...dodath scenn toscen todaig rogarg fiss goibnen aird goibnenn renaird goibnenn ceingeth ass:-
very sharp is Goibniu’s science, let Goibniu’s goad go out before Goibniu’s goad!" (Stokes, 1901)
He is also appealed to for protection in some early Irish charms which call on the art of Goibniu (O hOgain, 2006). This may relate to the idea that the being that created the weapon which caused the injury had power over the injury caused, something that we see in the charms relating to elf-shot.
Goibniu is especially associated with Cork, and in particular with Aolbach (Crow Island) on Beara peninsula (O hOgain, 2006). He was said to have his forge there and to keep his magic cow in that area. Other folklore associates him with county Cavan and the Iron mountains there (Monaghan, 2004). In later Irish mythology Goibniu became Gobhan Saer, a smith and architect of the fairies (Berresford Ellis, 1987).
In modern practice Goibniu is still seen as a smith God, but he also has overtones associated with the Otherworld and the sidhe, as do most of the Tuatha De. He could be called on to heal injuries caused by bladed weapons and possibly also by other weapons, and might be called on in conjunction with his two brothers by those who create with metal. I have called on him to bless weapons. Offerings to him might include beer, ale, or mead; I often offer him water, personally, as to me it makes sense to offer something cooling and refreshing to a God of the hot forge.
O hOgain, D (2006). The Lore of Ireland
Stokes, W., (1901). Thesaurus Palaeohibernicus : a collection of old-Irish glosses, scolia, prose, and verse
Berresford Ellis, P., (1987). A Dictionary of Irish Mythology
Macalister, R., (1941). Lebor Gabala Erenn
Monaghan, P., (2004). The encyclopedia of Celtic Mythology and Folklore
Stokes, W., (1926). The Second Battle of Moytura