Welcome to Fog City!
With a reduction in requests for fog and haze, the "smoky band" motif is becoming old hat as the industry looks for its next special effect. Some civic jurisdictions now won't allow smoke detectors in a venue to be disabled when an audience is present, negating the usage of fog or haze entirely. Regardless, the look does remain popular. Here is a general discussion of fluid types and their purposes, as well as types from which to stay away.
THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©
Fluids fall into the two general categories of "oil-based" and "water-based". Under that, they are subdivided into "Fog" and "Haze". Oil-based fluids are rarely seen today, but may still be encountered. These are not to be used in water-based machines, and although water-based fluids may be used in oil-based machines, it is possible that they may not provide enough pump lubrication. Conversely, using an oil-based fluid in a water-based machine may cause excessive build up and clogging. This usage is not recommended at all. Thus, it is suggested that to be safe, fluids should not be interchanged between machine types.
Note that dry ice (frozen carbon dioxide) is not included here. It makes fog by being placed in an enclosed drum of hot water where it produces a vapour of water droplets. Forced air is introduced to push the vapour out through a hose to the stage or other location. No fluid is required other than hot water. The disadvantage of this method is the cost, storage and transport of dry ice, plus the large amount of water needed and the power required to heat it. Typical sizes are in the 50 to 200 litre range for professional stage usage. Smaller ones may be encountered for disc jockey usage, but they have fallen out of favour because of low-cost fog-fluid machines.
These were the first to be used when non-dry-ice fog machines were developed in the 1930s and 40s. They work by being heated in a chamber which is enclosed, save for a fluid inlet and a narrow pin opening for the fog to emerge. As the fluid is heated to vapour point, the pressure rises in the enclosed chamber and the fog is emitted in a stream. Backflow into the fluid reservoir was prevented by a one-way valve.
The advantages of fluid units over dry ice were no storage problems, much smaller and lighter-weight machines, and lower power consumption.
The first fluid machines ran at much lower pressures and required an operator to walk around with one, or fans had to be used to disperse the fog throughout a given space. Later, these machines incorporated a hand pump used to pressurise the fluid in the reservoir so it could be forced into the heating chamber via a valve after sufficient pressure had been built up. This type of machine design lasted into the early to mid 1980s when they were succeeded by high-pressure, electric pump models, although recently some hand-pumped units have again emerged into the marketplace. Most, if not all, of the later fluid-based machines ones were/are produced in water-based models. (See next.)
A problem with oil-based fluids lay in their flammability. Given that the oil was heated, it was possible under certain circumstances for the fluid to ignite. Another problem was in the breathability. The fog bothered those acting or singing within it for long periods. Performers often complained that their throats were dried by it. These two drawbacks lead to the development in the 1980s of water-based substitutes.
Oil-based fluids are still available but rarely seen these days. Most often they are used in "crackers". These machines break up the fluid into a very thin, small-particle haze mostly used in motion pictures for atmosphere. Even these have been essentially superseded by water-based models.
These fluids are not flammable and are much more environmentally friendly to actors, singers, and the crews. The Rosco Company developed fluids based on alcohols that were water soluble. In the 1980s, they received a technical Oscar from The Academy of Motion Picture Arts and Sciences for this advance.
Since then, Rosco and other companies have come out with a variety of fluids that allow for Thick, Medium, and Minimal fog effects, along with Haze effects. Scented fluids were also introduced. The latter are not recommended because they can leave a residue which leads to early machine clogging. Few now seem to be available anyway.
Choosing the correct fluid depends on your purpose,
environment, and how quickly the fog must dissipate.
Here are some suggestions for each:
Note that some companies also offer grades of Haze Fluid, too. So one may choose minimal through maximum haze. As with regular fog fluids, minimal-effect haze fluids give the most tasteful effect, but they also dissipate the fastest; so choose appropriately.
One may also dilute the water-based thick-effect fluids with distilled water. Doing so will reduce the amount of fog introduced into the air, but this method is not much used today because many modern foggers have flow controls. However, it will not hurt the machine to dilute the fluids, although it's recommended to keep the dilution under 25%. Be sure the dilution medium is distilled water, not from the tap. Tap water can cause scale to build up and clog the machine.
Never use fog fluid in a hazer or vice-versa unless the fluids
are specifically designed for a given type of machine. Generally,
fog fluids are meant to be heated, while hazer fluids are not.
There are many cheap fluids out there. The chief difference is that they are often over diluted (giving a less-than-expected effect), and that they have a higher "residue after evaporation" specification. This means that after fog is generated, there is something left. This "something" will eventually lead to clogging. A way to test a fluid is to take an aluminum pie plate, place a few drops of fluid in it and apply heat. Don't boil or burn it. Gently heat it until no more vapour is being produced, then allow the plate to cool. Inspect the remains. The better fluids will leave far less residue with no grit.
Another concern lies with haze fluids meant for usage in non-heating machines. These machines don't heat the fluid but instead "vibrate" it into a small-particle haze. With these machines, it's possible for bacteria to be introduced into the air because there is no heat to kill it. Be sure to keep these fluids tightly capped. Used fluid should be kept in a separate container and consumed first. This is to keep "poured-back" bacteria at a minimum and to prevent contamination of fresh fluid. These types of machines should be regularly cleaned in a ventilated or outdoor area using a diluted bleach-based solution.
One final thing of which to be aware is that some companies
are selling "short" gallons and some dealers are using the
nondescript term `jug'. Always ask for, and demand, that
all quantities be given in litres so you will know how much
fluid you are actually getting.
Fog and Haze Fluids
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