As you would guess, drycleaning is called drycleaning because it doesn't use water. However, drycleaning is done with a liquid solvent, so in effect the cleaning does get wet, but not with water. It's an important distinction. Water penetrates the fibres of the fabric making them swell, causing felting and shrinkage with some fabrics. The solvent cleans each fibre without the swelling and so felting and shrinkage do not occur.
Also, the cleaning is not normally immersed in the solvent as it is in the water of a washing machine. Instead the solvent circulates through the cleaning, and a series of giant filters remove any insoluble soil. Clean solvent is used in every load. The dry-cleaning process is so gentle almost every fabric can be safely cleaned, from suits to the most delicate of silks and linens.
The average Christchurch drycleaner's machines are probably about two metres high, two and a half metres long and from the front look somewhat like giant front-loading washing machines. Everything to be drycleaned has to fit in the machine.
You can find out a lot more about drycleaning in our archived newsletters. You can use the search function to find the topics you want.
Unlike water, which requires a detergent in order to clean, drycleaning solvent is the actual cleaning agent. It is quick and efficient and excels at removing grease, soil and general grime. With a little pre-treatment even stains like lipstick are easily removed. Where a stain comprises different ingredients, drycleaning takes out all the grease or fat but can leave the residue behind as a white powdery deposit. Each garment is inspected after it comes out of the machine and such deposits are easily removed at this stage.
So if you get your clothing back from the cleaner and you see a white powdery mark that you are sure wasn't there when you sent it in, you can be assured that it was there, it's just that it wasn't white so you hadn't noticed it. However, your drycleaner obviously missed it when he was checking the garment. Send it back to him, as it is easily fixed, often just a second or two, with maybe a re-press to tidy up the finish.
In most countries including New Zealand, most drycleaners use a solvent called perchloroethylene, or "perc". It looks just like water, but is nearly twice as heavy. Interestingly, its made from coke, although exactly how my book doesn't say. This means that it's a mineral based product somehow derived originally from coal. It is a very effective cleaner.
We are occasionally asked about how much solvent we use, and what happens to all the used solvent? After all, it's OK for dirty water to go down the drain but solvent is another matter.
Strangely, the basic answer is that although drycleaning is done with solvent, a modern machine uses up almost none. This is because after each load the used solvent returns to a distilling tank where it is turned into clean solvent for re-use. We have estimated we re-use the same solvent 1700-1800 times. Imagine how long your water would last if your washing machine did that! Usually once a week the drycleaner scrapes the accumulated soil out of the bottom of the distilling tank for disposal.
Modern machines are so effective in recovering the solvent, that at Eastern we calculate that we use about 2ml of solvent per kilogram of clothes cleaned. That's not much, and is less than one ml for a pair of trousers. So interestingly, although the solvent costs around $700 per drum, we spend little more on solvent than we do on staff morning tea supplies.
In the past there's been some very strange products used as drycleaning solvents, so we'll talk about some of the interesting ones in future newsletters.