There are three general types of film, categorized by their general purpose and the kind of chemicals needed to develop them.
The most common film we know of is called the negative film or color film. These are the ones we normally buy in stores. When we have them developed, what we get together with the photos are the negatives (hence, negative film). I suppose you know how they look like. On the box of a negative film, you will find the code, C41. This indicates the kind of chemical to be used in developing negative film, C41 chemicals.
Another type of film goes by many names. Color reversal film, positive film, slide film, chrome film, pertains to the same kind. They are not normally intended for photo prints, unlike negative films. They are meant to be used as a projector slides. When this type is film is developed, you do not get a negative, but instead a positive (hence, positive film). If you view it against light, you can already see the image, as it is supposed to be. Each frame is normally mounted as a slide (hence, slide film). If you are familiar with carousel projectors (a technology popular before the age of PowerPoint presentations), they use these slides to project images onto to a screen or wall. In movie theaters, motion pictures are projected from a reel of film; such is more or less the same material as slide films. This type of film is developed using E-6 chemicals, as indicated on its box.
Lastly, we have the traditional black and white films. They are of course used to take black and white photographs. Although there are many black and white films in the market that can be developed using C-41 chemicals, traditional B&W films are developed using B&W chemical.
Now, hopefully you have been enlightened somehow about the different types of films. Your knowledge of them will help you in understanding the technique of cross processing. We now know that each type of film, negative, slide, and traditional black and white, are developed using specific chemicals. Technically, cross processing refers to using wrong chemicals in developing a particular film type. If you use C-41 chemicals in developing slide films, if you use E-6 chemicals in developing negative films, if you use black and white chemicals in developing slide or negative films, you are cross processing! You are processing the film with the wrong chemicals. Although, there are several means to cross process, the most commonly used is the use of slide films which are developed C-41 chemicals, instead of E-6. The result of which, I have loosely described in my opening paragraph. It is also the service easiest to avail. Not too many photo labs have E-6 chemicals to be used in developing negative film, and if there are, it’s more expensive.
How to Have Your Slide Film Cross Processed
Some hardcore lomographers and advanced film photographers develop their own film. In their own dark room, they can cross process anything! What about the beginners and those of do not have laboratories of their own? They can still experience the joys of cross-processing. It’s quite simple. After you have finished a roll of slide film, simply go to a photo laboratory, and ask the personnel to have the film developed, as though you are having a regular negative film developed. Specify that it is a slide film which you would like to be cross processed or developed using C-41 chemicals. If he knows what he is doing, he will accept that without questions. If not, he may hesitate, or he may insist that they do not have E-6 chemicals. Simply assure them, that you exactly what them to develop the slide film using C-41 chemicals. If he still insists on not accepting it, better look for another photo lab. Here in the Philippines, Digiprint branches accept slide films for cross processing, with no questions asked, and for a very cheap price! Some labs offer you the choice of either photo prints, or simply scanning the film and burning it to a CD. Personally, I go for negative scanning. Once I have seen the soft copy, them I will choose which images I would like to be printed.
Generally, slide films are more expensive than negative films. They are also less available. But if you search hard enough, you will find them. I normally get mine from the Internet. Lomography forums in your locale usually have people who sell slide films and other lomographic items. Just be careful with your online transactions. Look for expired ones, they are cheaper. Many say that they also give out the craziest of colors. I have already used films that are 5 years expired; they are still as good as ever. Different brands are also known for different dominant hues in the images. For example, Fuji Sensia 200 normally comes out greenish in color. Try different brands, and have yourself surprised with the wonderful colors that cross processing bring.
Is Xpro Equivalent to Lomo?
The short answer to this would be, NO! It is however a misconception that is very common. I myself made the same mistake early on. There is just such a strong association between the two. At the same time a substantial percentage of lomographers do cross processing. They however argue that the use of negative film (not cross processed) is also lomographic, provided that you spend it with the lomographic attitude! Using black and white film and red scale film are also popular among lomographers. I will discuss them soon in my succeeding write ups.
For now, go get yourself some slides, and experiment with cross processing! Enjoy!