How a vinyl record is pressed
Galvanics & Processing
Once the master lacquer has been cut it is ‘processed’ into metal ‘stampers’ that are used on the pressing machines.
Firstly, the lacquer is cleaned carefully using a washing system where no human contact is made other than with liquids. The lacquer is then ‘sensitised’ in a liquid ‘dip’ preparing the lacquer for ‘silvering’.
‘Silvering’ is where the lacquer is placed on a slowly rotating vertical turntable and sprayed with a very fine silver nitrate spray. This penetrates the lacquers’ grooves with exact accuracy and prepares it with a metal surface ready for the electro-plating process.
This process involves the silvered disc being submerged in a nickel solution and connected to the electric terminals for the plating procedure. This deposits nickel onto the silvered disc and goes on for one and a half hours. After this process, enough nickel has been plated on the disc to support itself. This is called a ‘negative’, as it is a mirror image of the lacquer.
This negative is cleaned and coated with a ‘passivator’ and then goes back into the plating baths to make a ‘positive’ by the same electro-plating process.. This is the positive, which is an exact playable copy of the master lacquer.
After separation from the negative, the positive goes into the plating baths. The same process is applied to make the ‘stampers’.
Several of these can be made from the positive. Generally one stamper is good for around 1,000 records, before it splits in the press or is worn out / discoloured.
After separation, the stamper is trimmed and ‘formed’, ready to be fixed into the press.
Mastering & Cutting
Once the audio is complete and saved as a file (wav/aiff) it will be sent to our vinyl cutting suite where it will be mastered.
The mastering involves playing the audio through a series of EQ’s (where treble, mid-range and bass content can be altered) and compressor/ limiters. The levels are controlled by reducing the impact of peaks/transients in the audio. This means a louder sounding signal can be cut.
Multiband (the signal split into treble/ mid/ bass) compressors/ limiters can also be used. If there are one or two loud crash cymbals or sibilant vocals, these can be reduced with careful set-up, so as to not reduce the specific frequency for the whole track.
Once a good mastered sound is achieved the audio is cut onto a master lacquer. This is an acetate coated aluminium disc, 14” diameter. This is achieved by sending the mastered audio to the cutting amp rack.
Here the signal is first passed through the RIAA curve system and then into 2 power amplifiers. These are high quality audio amplifiers, around 600watts per channel (left and right).
This amplifies the audio from the line level input and sends the signal to the ‘cutting head’. The cutting head is two very accurate, small, loud speakers with magnets which drive 2 metal rods (1 per channel). These two ‘drive rods’ meet at the cutting stylus, which can be driven in both the horizontal (level) and vertical (stereo) axis.
The master lacquer is rotating at the specified playback speed, and the cutting head is lowered onto it. The cutting head is pushed across the rotating lacquer by the ‘vari-groove’.
This piece of equipment listens to the audio signal and pushes the head across the lacquer at a higher or lower rate depending on the audio level. This ensures that cutting grooves in the record do not crash into each other, and that disc space is maximised in quiet passages.
The cutting head is tipped with a sapphire cutting stylus and cuts the soft lacquer out of the rotating disc, by moving up and down, left and right, as the lacquer rotates beneath it, tracing out an exact waveform representation of the music/ input.
Pressing
Vinyl records are pressed by introducing the raw material (PVC) into the press where temperature and hydraulic pressure squeeze the raw vinyl into the shape of the stampers leaving the imprint of the original master lacquer.
The stampers are fixed to ‘moulds’ in the press, one for each side of the record. These steel moulds contain a labyrinth of tunnels inside them where steam or cold water can be introduced under high pressure to control the temperature exactly during the pressing procedure.
Firstly, the raw vinyl is heated and formed into a ‘puck’. This is a hot, soft slab of vinyl PVC, with weight content a little more than that of the finished record. This is introduced into the middle of the press. Then the record centre labels are placed above and below this puck on a ‘label arm’. ‘Centre pins’ (top and bottom), come through the centre of the moulds to hold the labels in place and stop vinyl filling the centre hole. The moulds are heated with steam to around 140 degrees, the press closes utilising a hydraulics system, to around one ton of pressure.
Under this pressure and heat the puck is squeezed out and fills the space exactly between the stampers. After a few seconds the steam is replaced with cold water, this allows the record to become firm enough to be removed from the press.
This record is then placed on the ‘trimming turntable’, where excess vinyl is cut away to leave a 12” disc. This, once cooled, is ready to play.