Oil

The oil used by Tel-ray (and later Morley) to record electrostatic sound recordings was the object of much debate and speculation and that is not without a reason. In general, the device will not work correctly without the proper oil. Theoretically, the charge transfer is possible without oil, but the recording quality will be poor, and the wear on the recording surface will be significant.

There are two main functions of oil in electrostatic recording:

Bridge: Oil serves as a bridge between the recording head and the surface, allowing the transfer of charge.
Lubrication: It reduces friction between the recording head and the surface, preventing wear and tear.

It is important to understand the properties of oil used in electrostatic recording, as they can significantly affect the performance of the recording system. The key properties to consider include:

Viscosity: Affects the flow of oil and the thickness of the oil film. The viscosity should be low enough to allow for easy flow but also high enough to maintain a stable film.
Conductivity: Determines how well the oil can transfer charge. The conductivity of the oil should be low enough to prevent loss of resolution of the signal but high enough to allow for effective charge transfer.
Adsorption: Influences how well the oil adheres to the recording surface, which is crucial for maintaining a consistent recording quality.
Volatility: Affects the evaporation rate of the oil, which can impact how often it needs to be replenished.

Conductivity

If the oil conductivity is too low, the recording will not work at all, as the charge will not transfer effectively. If the oil conductivity is too high, the recording will be poor, as the signal resolution will be low. This comes from the fact that the oil bridges the recording head and the surface, allowing for charge transfer. Yet, the high conductivity will form a bridge that is too conductive, leading to a loss of resolution. Figuratively speaking, the heads see through the oil as through the lens of a camera, if the oil is too conductive it will allow to see too much, leading to a blurry vision of the signal.

PCB Oil

It was a matter of debate whether PCB oil could be used in electrostatic recording. However, it is now known that PCB oil is not suitable for this purpose due to its high viscosity and poor electrical conductivity. Instead, other oils with better properties are recommended.

It is also interesting to analyze how the myth about PCB oil being suitable for electrostatic recording originated. It is likely that the myth arose from the fact that PCB oil was commonly used in various industrial applications, and its properties were not well understood in the context of electrostatic recording.

Microemulsions

Microemulsions are thermodynamically stable mixtures of oil, water, and surfactants. They can be used in electrostatic spraying to improve the deposition of oil on surfaces. The key components of a microemulsion include:

Oil phase: Provides the hydrophobic component.
Water phase: Provides the hydrophilic component.
Surfactants: Reduce the surface tension between the oil and water phases, allowing them to mix and form a stable emulsion.
Co-surfactants: Enhance the stability of the emulsion by further reducing surface tension.

Working examples

Chemical name	Other names	Availability	Conductivity	Adsorption to oxide
Pentapropylene glycol n-butyl ether	UCON LB-65, PPG-5 buteth	Poor (only available in bulk)	Moderate	Excellent
- Excellent
Tripropylene glycol butyl ether	TPGBE, PPG-3 buteth	Moderate (available mostly from chemical suppliers)	Moderate	Excellent
Polypropylene glycol n-butyl ether	(Generic) Compressor PAG	Good (available from aftermarket suppliers)	Low	Good
Triethyl citrate	TEC	Good (available from chemical suppliers and some DIY cosmetics suppliers)	Moderate	Good
Glicerol triacetate	Triacetin	Good (common solvent)	Moderate	Poor

Pentapropylene glycol n-butyl ether (UCON LB-65)

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Tripropylene glycol n-butyl ether (TPGBE)

Safety data sheet

Product	Amount	Distributor	Region	Price	Price per litre
Tri(propylene glycol) monobutyl ether	1 l	Carl Roth	EU	€52.70	€52.70
Dodatek przeciw krystalizacji Black Arrow	250 ml	Black Arrow	PL	40 PLN	160 PLN


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Links: - Dow oxygenated solvents - "Glycol ethers" section

Triethyl citrate (TEC)

Product	Amount	Distributor	Region	Price	Price per litre
Triethyl citrate, 1 l, glass	1 l	Carl Roth	EU	€42.90	€42.90
TEC Cytrynian trietylu	100 ml	Chwasciarnia	PL	27.93 PLN	279.30 PLN

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Triacetin

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Oil