Spots caused by hard water, acid rain and other staining agents have always been a problem on automobile glass. Most detailers try plain glass cleaner and go no further. Others sometimes try methods that may damage the glass itself. But there are safe ways to remove most spots.
Let's start by exploring hard water. Elements such as calcium, magnesium or iron give water undesirable characteristics we call "hardness" that cause spotting on glass (and paint). Calcium ions are formed by a reaction of calcium carbonate (limestone) and carbon dioxide in wastewater. Hard water, also sometimes called acid rain, is only part of the problem. There is also a chemical reaction between these minerals and commercial fertilizers which can leave a cement-like deposit on glass. Acid rain, a result of environmental pollution, when mixed with water creates an acid that can spot or even etch glass.
Commercial window cleaners use acid-based cleansers similar to those detailers use to clean wheels. The acids can be a quick and easy way to remove many stains and spots from windows, but they do require understanding and caution in their use. There are two types of acids: organic and inorganic. The inorganic group includes hydrochloric (HCI) and hydrofluoric (HF, also called muriatic) acids. Organic acids are active or "critic" and are derived from fruit. They are used in colas. (Makes you want to put that Coke away, doesn't it?) An inorganic acid can lift, suspend and dissolve water spots.
But not all acids are equal and many experts warn against using HCI or HF to clean glass. Not only are they dangerous to the glass, but also to you. Getting such acids under your fingernails can result in loss of the nails or worse. Getting some acid in your eyes, or breathing its vapor, can result in serious injury. There are a number of alternatives to the use of inorganic acids. One technology uses a base of phosphoric acid, with buffers that help prevent danger to the user. Another is a thick liquid that clings to the glass. It is a combination of safe acids and non-scratching abrasives. There is also a powdered product that can be made into a paste and then applied to the glass. Some companies offer a glass polish cream that has a light, non-scratching abrasive that works well with no danger to the glass or the user.
As with any job in the detailing process, we must apply a little science in the glass cleaning process. These are the steps to follow:
* Identify the type of glass. It is not certain all glass is the same on all cars. First test a small area to see if the product you are using could damage the glass on your Porsche. You may also have non-glass windows: thermoplastics such as Plexiglas, often used for convertible rear windows. When choosing the chemicals and procedures to clean them, remember they are very fragile.
* Identify the type of stain. You must identify the staining medium and the length of time it has been on the glass. The longer it has been there, the more difficult it will be to remove it. Some spots can not be removed without damaging the window. For example, pitting and etching from acid rain may look like spotting, but is really damage to the glass. In most cases these spots cannot be completely removed, though their appearance can be altered.
* Choice of product. Once you have identified the glass and the source of the problem, you can choose the appropriate chemical(s). Obviously, you will need to have several products available to deal with the various types of surfaces.
In summary, remember that removing water spots is not a simple cleaning job that can be done as a routine part of a detail. It is a restoration process that may require a great deal of time and, as mentioned, you may not always be successful.
Staying on the subject of glass, I'd like to mention a service which I personally have used and am very impressed with: Etching its VIN number on your Porsche's windows. During my discussions with various peace officers I know, they all considered it an effective deterrent against theft. No one will purchase that glass from a thief. I also received a 5% discount off the "comprehensive" section of my car insurance, paying for the cost of the job right away. The kit was mailed to me and it took me literally five minutes to do six windows plus the sun-roof. My cost was only about $30. I realize this won't make my car 100% theft-proof, but anything we can do to make a thief move on to another car is worth the investment.