Yes, the very best laminated sword blades which had no inserted hardened steel bar for the edge did have to have carbon re-infused into the edge and tip by heating the blade in a charcoal packed oven. Once the carbon in the edge was high enough the blade was then ready to be tempered.

Unlike today's heat treatment procedures which use thermally accurate oven temperature controlled thermostat treatments and even controlled cooling over considerable time and sometimes cyrogenic cooling to reduce stress in the blade...back then the tempering was all done by hand and eye... it was this skill of judging the temperature of the blade that made the difference between a master swordmaker and an "also ran"...to say though that they had this mastered is a bit "trite" and something of a understatement...

A detailed and complex vocabulary was created to describe the various colours of the steel through the heating process...even poetry was written on the topic...using fiercly guarded skills of clay and water painting on the blade ( sabidoro) a sword master could create the perfect differentially hardened steel blade.

The clay in differing thicknesses protected the steel so that it was heated and cooled at differing rates...each purposefully done so that the hardest steel was created at the edge but it was protected by softer steel at the spine and sides...enabling it to survive strikes from other swords without shattering...and if done properly cut through armour and other lesser swords...judging the state of the steel during the temper was an art and gave rise to poetic descriptions such as " Heat the steel until it is the colour of the moon rising in the June sky"...meaning the edge was white hot but the golden hughes of the sabidoro covered steel were like the golden hue of a summer sky at dusk...not only was poetry a part of the riddle of steel but also prayer...when the steel was hammered it would be done to the rhythm of prayers said over the sword...Bushido in it's fundamental state...to a Japanese Samauri his sword was a reminder and affirmation of man's pursuit of perfection...

Once made the sword would be signed by aspiring makers but often never signed by the best master's...their blades were easily able to be recognised as their work by those who could appreciate them...and those who could not did not deserve to enjoy them. Because of this reluctance to sign the best blades and the fact that travelling engravers would be needed to do the signature....and were also used to cover up minor blemishes or defects with engraving the best makers were reluctant to be associated with an engraver... all expensive blades,once made, were then subjected to independant testing and graded on their strength,balance and sharpness. Those that passed with the highest honours were then signed by the tester and the signature was inlaid with gold. Only once graded to this standard would the owner of the blade of a "master"" ever return to the master and ask for his signature as a favour or honour...knowing that this blade would become his family's sword for generations to come and would be the biggest legacy he would pass on...but many of the best blades were never signed and instead were "named"....those blades became "legends".