In the context of vinyl record production, a lacquer refers to the initial disc that is cut in a studio by a sound engineer and will serve as the basis for the rest of the production. This is the lacquer that is cut during the cutting process. Here is technically its manufacture:
Aluminum plate preparation: The process starts with the preparation of a thin, circular aluminum plate, called a "Master". This plate is polished until it achieves a perfectly flat surface, with a tolerance of 10 to 20 microns.
Lacquer application: A special lacquer is then applied to the aluminum plate in a clean room. This lacquer has a unique composition, designed to meet the strict requirements of disc production. It is applied at a thickness of 180 to 200 microns. The lacquer used must have a certain flexibility to allow the cutting process, while being hard enough to faithfully reproduce the sound signal.
Inspection and drying: After cutting, the lacquer is inspected and left to dry. Only lacquers that pass inspection are shipped.
It is important to note that the manufacture of lacquers is a delicate process that requires a high level of skill and expertise. Moreover, there is only one company in the world that manufactures lacquers, Public Records in Japan.
There are three types of lacquer cutting: standard cutting, half-speed cutting, and 100% analog cutting.
Standard cutting is the most common process, used for most LPs, EPs, and SPs. The master and the cutting system operate at the original speed of the recording.
Half-speed cutting slows down the cutting process, giving more time to engrave the smallest details of the music. This improves the dynamics, bandwidth, and recording level, and is often favored for audiophile records.
100% analog cutting, as its name suggests, is done from a master tape and does not go through any digital stage.
The lacquer cutting machine, like the Neumann VMS 80 for example, works by using a cutting head that is heated. This cutting head is equipped with a stylus, usually sapphire, which vibrates at high frequency. When the lacquer is placed on the machine, the technician sets the desired rotation speed 33rpm or 45rpm and the heated stylus penetrates the lacquer slightly melting the nitrocellulose layer to create a groove. The vibrations of the stylus are controlled by the audio signal that is sent to the machine via an amplifier and a RIAA converter, which allows to engrave the frequency and amplitude variations of the sound in the groove. During this process, the machine uses a cooling system, usually helium, to prevent the cutting head from overheating due to the friction created by the rapid vibrations of the stylus. Finally, the debris generated by the cut is sucked up by a suction system to avoid any interference with the cutting process.
In terms of technical characteristics, a standard cutting machine has a frequency response from 20Hz to 18kHz, can engrave vinyl records of 5, 7, 10, and 12 inches at recording speeds of 33, 45, and 78 rotations per minute, and can engrave up to 19 minutes per side on a 12-inch record at 33 rotations per minute without loss of level if the mastering is suitable. The device is equipped with a diamond cutting head and a heating stylus and has a central unit for RIAA encoding, groove control, and stylus temperature control.
It's important to note that there are certain inherent limitations to vinyl cutting. The first concerns the duration of the music engraved on each side of the record. The more music on one side, the lower the volume of the record will be. For example, it is recommended not to exceed 9 minutes of music for a record spinning at 45 rotations per minute and 19 minutes for a record spinning at 33 rotations per minute if you want to achieve loud sound. It is also recommended to distribute the tracks well on each side of the record, for example by avoiding putting 6 minutes of music on side A and 18 minutes on side B because the cutting level will be calculated on the longest side.
Secondly, extreme frequencies can pose problems during cutting. Low frequencies take up more space than middle and high frequencies, and if they are too high, the cutting head can heat up or cause "clips" on the recordings. It is therefore advised to avoid all frequencies above 16 kHz.
Then, phase problems can occur if you use too much amplitude on stereo effects like phaser or flanger. An excess of amplitude of these signals, especially on low frequencies, can cause a great amplitude of the diamond in depth during the cut, making the groove thinner at some places and risking to make your cartridge "jump" during the playback of your vinyl. This can always cause unpleasant listening effects, even if these signals can pass on some turntables and not on others.
You should also be careful not to push your masters to the limit of saturation to have a louder sound on your vinyl. This is pointless, as any distortion will be amplified during the cut. In addition, the digital volume of your masters has nothing to do with the volume of your future vinyl, which depends on the total time of your sides, your frequency range, and the dynamics.
Finally, it's important to note that the thickness and weight of the vinyl have no impact on the final sound. So there's no sense in thinking that a heavier vinyl has a better rendering.
In summary, vinyl cutting is a delicate process that requires particular attention to technical details and inherent limitations of the medium. However, with a correct understanding of these factors, it is possible to create high-quality vinyl recordings.