There have been some statements made which I have overheard that need correction. The reason that these are being presented here are that they seem to be present in more than one situation by more than one person. There are three elements of the sword which are going to be discussed here, fullers, piercings and cross-guards or quillons. The reasons for these discussions will become clear as the discussions proceed.
1. The Fuller<https://fightschool.eu/h2>The fuller is a shallow channel which you will find present on some swords. It is most likely found on swords with a wide blade. It has been referred to some as a "blood groove" with the explanation that it allows the easy withdrawal of the sword when thrust into a person. It is not<https://fightschool.eu/i> a "blood groove" at all.
2. Piercings<https://fightschool.eu/h2>The piercings which are being spoken about in this case are through the blade. The purpose of these piercings are both to lighten the weapon and they were also added as decoration. There are examples of this being performed on rapiers from the approximately 1590s onward. This feature was, again, added during the manufacture of the blade, not as a post-manufacture modification of the weapon.
The purpose of the fuller is to lighten the weapon while strengthening it at the same time. This feature of the blade is added during the construction of the blade. Attempting to add a fuller or fullers post-manufacture will weaken the blade, possibly in two ways. The first way is that by taking metal away from the blade it weakens it, and the second method is by heating the blade, especially by grinding or other modern methods, this can affect the temper of the blade.
Just as with the addition of a fuller or fullers, above, the post-manufacture addition of piercings to a blade will weaken the blade and shorten its potential life and for similar reasons to the addition of post-manufacture fullers. The removal of metal from the blade creates an inherent weakness in the blade, also the creation of any piercing by modern means will, again, create heat which can affect the temper of the blade around the area in which the piercings are made, thus creating weakness.