Na ferraria padrão, a fim de reformar uma lâmina como essa, é mais do que apenas "colocá-las lado a lado e fazer o possível para selá-las". Normalmente, você aquece a extremidade do fragmento até que o metal esteja amolecido, pega o fragmento que ainda está frio e duro e o insere no metal amolecido. Então você aquece a costura e a sujeita a revenido: velho ferreiro batendo nela com um martelo. Isso produz uma junção bastante robusta, mas a costura é sempre visível e a espada nunca é tão robusta quanto era originalmente. No entanto, isso não era padrão. Era um elfo ferreiro.
Do Silmarillion, "Dos Anéis do Poder e da Terceira Era":
The host of Gil-galad and Elendil had the victory, for the might of
the Elves was still great in those days, and the Númenóreans were
strong and tall, and terrible in their wrath. Against Aeglos the spear
of Gil-galad none could stand; and the sword of Elendil filled Orcs
and Men with fear, for it shone with the light of the sun and of the
moon, and it was named Narsil...
But at the last the siege was so strait that Sauron himself came forth; and he wrestled with Gil-galad and Elendil, and they both were
slain, and the sword of Elendil broke under him as he fell. But Sauron
also was thrown down, and with the hilt-shard of Narsil Isildur cut
the Ruling Ring from the hand of Sauron and took it for his own...
Thus Narsil came in due time to the hand of Valandil, Isildur's heir,
in Imladris; but the blade was broken and its light was extinguished,
and it was not forged anew. And Master Elrond foretold that this would
not be done until the Ruling Ring should be found again and Sauron
should return; but the hope of Elves and Men was that these things
might never come to pass.
Da Irmandade do Anel, cap. 3, "O anel vai para o sul":
The Sword of Elendil was forged anew by Elvish smiths, and on its
blade was traced a device of seven stars set between the crescent Moon
and the rayed Sun, and about them was written many runes; for Aragorn
son of Arathorn was going to war upon the marches of Mordor. Very
bright was that sword when it was made whole again; the light of the
sun shone redly in it, and the light of the moon shone cold, and its
edge was hard and keen. And Aragorn gave it a new name and called it
Andúril, Flame of the West.
Nunca nos dizem como os elfos reforçaram a espada; eles podem tê-lo remodelado completamente e reformado uma nova lâmina; eles podem ter feito algo parecido com o que um humano teria feito (é assim que Jackson o mostra na edição estendida Return of the King). Nós sabemos pela descrição que era uma lâmina poderosa, com as propriedades mágicas da luz solar e da luz da lua.
Das Duas Torres, Cap. 7, "Profundidade do Leme":
Charging from the side, they hurled themselves upon the wild men.
Andúril rose and fell, gleaming with white fire. A shout went up from
wall and tower: "Andúril! Andúril goes to war. The Blade that was
Broken shines again!" ...Three times Aragorn and Éomer rallied them,
and three times Andúril flamed in a desperate charge that drove the
enemy from the wall.
Isso parece indicar que não perdeu nenhum de seus poderes desde a Primeira Era; só podemos assumir que é porque foi reformado pelos elfos. Não vamos esquecer que um dos ferreiros deles forjou os Três. Eles eram definitivamente talentosos nessa área, possivelmente até de uma maneira mágica. A partir das descrições dadas, parece que não era mais fraco ou mais forte, mas o mesmo poder.