In order to guarantee the long-term functionality of a Lange watch, it should be serviced by a qualified watchmaker at regular intervals. In the course of this rejuvenation, great attention is also devoted to the case. A. Lange & Söhne uses an overhaul method that is non-invasive and extends the service life of the individual case components: repair welding by laser-based material application. Regardless of the age of the watch and the use of gold or platinum as a case material, nearly all types of damage involving the removal of material can be repaired like this.
Preparation of individual parts
First, all of the types of damage sustained are recorded. The components of the case are thoroughly cleaned. After drying, damage repair intervention begins. Smaller, shallow nicks are eliminated with grinding and polishing while laser-repair is the technique of choice for deeper scratches or dents.
A metal wire with a diameter of 0.1 millimetres is melted onto the damaged area with a high-intensity laser flash. The wire is made of exactly the same material as the case. Scratches and scoring can be filled in such a manner that the laser-repaired areas are no longer detectable after polishing. Any excess material at the lasered points is subsequently ground off and smoothed.
Depending on how large the affected area is, grinding will be done manually or very cautiously with a machine. Prior to this step, flawless surfaces are masked with tape to prevent unintentional damage. The manual grinding sequence requires emery paper of various grit sizes. The direction of motion is changed regularly. For the final pass, the grit size is roughly equivalent to one fiftieth of the diameter of a human hair.
Polishing with a goat hair and cotton wheel
To seal the ground surfaces, they are initially buffed with a rotating animal hair brush and polishing paste. To restore the original appearance of the case parts, they are polished yet again. The use of a cotton wheel and polishing paste produces the desirable mirror gloss. Gold alloys can be ground and polished much faster than platinum because the latter is considerably harder and tougher than gold.
After all flaws have been eliminated and the parts are cleaned and dried anew, the watch is re-assembled. The final inspection assures that all damage has been repaired and the watch leaves the manufactory in mint condition. It now looks like new and is ready to serve its owner in its original splendour.