The term "alternative", in this context, mostly refers to processes dating from the dawn of photographic history. Their remaining interest in the 21st century, and the subsequent revival in their use, is partly in reaction to the ever greater perfection attainable with current technology, and a desire to work with materials which bear the marks of the creative process.

Photographic pioneers of the 19th century hand-mixed their own processing solutions from raw chemicals of often dubious purity, and photosensitive plates and printing papers had to be hand coated, often in several stages.  The process was slow, laborious and fraught with opportunities for error.  And, on top of that, the light-sensitivity of the materials was poor - necessitating camera exposures of many seconds and, for printing out, several minutes in sunlight.  So it's easy to see why these early techiques fell by the wayside in the onward march of technological progress.  Commercial photographers need accuracy & repeatability in their materials and to be one step closer to the unattainable goal of perfection than their competitors.  But for fine art use the opposite is often the case.  The hands-on approach brings with it a knowledge of what individual materials can do.  "Faults" become "characterisics" and "time-consuming" simply implies that there's time to change things as the whim takes you...

One factor which all these historical printing processes have in common is that the printing paper, once coated and dried is very insensitive to light - 10 minutes in bright sunlight is the typical requirement for complete exposure. There's no way that this intensity of light can be projected through a tiny negative in a conventional enlarger, so all of these processes require a negative of the same size as the final print.  In days of old, box cameras used 10x8" glass plates (& later film of the same size), so the negatives were already sufficiently large.  In modern times film sizes have become smaller, though you could always use a pinhole camera with 5x4" film, or use an existing photograph & print a negative on OHP transparency film with an inkjet printer - a novel mix of new & old technologies!

I'm not an expert in historical processes and this page is intended only as a brief introductory overview.  For a good practical guide & survey of what's possible, I'd recommend Richard Farber's book: "Historic Photographic Processes", Allworth, New York, 1998.  There's also a vast amount of technical information available elsewhere online, with an increasing amount of practical material on making large format negatives from digital files.  I won't list links since they become outdated!  Just search...

about cyanotype prints

Cyanotype is one of the many non-silver based photographic printing processes developed in the early days of photography and is instantly recognisable by the deep blue hue of the prints produced.  The basic formula was invented by Sir John Herschel in 1842 and quickly found favour with botanical illustrators including Anna Atkins.  Later, this became the "blueprint" process by which engineering drawings were reproduced (& which Robert Rauchenberg & Sue Weil famously used for their "female figure" photograms in 1951).   The cyanotype process requires plain paper to be coated with the sensitizer solution before being exposed to intense light through a full sized negative.  The print is then made permanent by washing in water.  Ready-coated blueprint paper is no longer available, the process having been replaced by the diazo positive printing method in the 1960s, but it is possible to buy pre-mixed senstitzer.   After some experimentation I've settled on using Dr Mike Ware's variation of the fomula which is available in a pre-mixed solution from Fotospeed.

The process is quite particular about paper type.  Many of the archival watercolour papers are soaked in an alkaline buffer solution as part of the manufacturing process, and this does cause problems with staining in the highlights.  I've found that coating the paper with weak citric acid solution (about 4% w/w) beforehand, allowing it to dry & then applying the sensitiser, does the trick.

about salt prints

Salt printing is one of the earliest photographic printing techniques and dates from 1833.  This is the process by which photography pioneer William Henry Fox Talbot produced the first photographic images on paper.  The process involves first soaking a sheet of plain paper in salt water before brush coating it with a silver nitrate sensitizer.  When dry, the paper is exposed to intense light through a full size negative and the image slowly begins to form over a period of 10-15 minutes.  The print is then made permanent by washing in a conventional photographic fixing solution.

As with the cyanotype process, chemicals in the paper can cause problems. Start with Arches Aquarelle, 300gsm HP (smooth) which is available from most art supply shops.  Fabriano Artistico HP also works well.
Do wear gloves & safety specs when handling silver nitrate solution, it permanently stains skin and eye tissue (& clothing, carpets, etc.)  But actually, this is about the least noxious of all the alt processes apart from that!

If you're going to try these processes, you will need...

ultraviolet light

The simplest source of UV light is our nearest star, the sun; & for the quality of light, it can't be bettered!  The only problem is that it can't be switched on or off at a whim & its intensity is subject to the vagaries of our weather.  Clouds have a tendency to appear from nowhere at about 8 minutes into a 10 minute exposure...  Far more reliable is a UV light box.  Try to avoid the type with many tubular lamps laid close to the glass surface, as any imbalance between tubes results in banding of the final print.  In fact, a single lamp suspended about 1m above the print will give a good illumination.  DO NOT USE lamps intended for sterilization purposes or electronic chip erasure - they emit UVC (& not much else) nor the "blacklight" type lamps used for glow-in-the-dark effects in dance clubs.  Neither will work, and the sterilization type will blind you, poison you with ozone and burn your skin in the process!  The best easily available option is a lamp intended for sun beds or tanning purposes.

Osram (used to?) manufacture something called an ultra-vitalux, which claimed to emulate sunlight in that it had both an 80W mercury vapour capsule + a 200W tungsten filament lamp in a single package.  But for requiring an ES lamp holder, it could be connected directly to household power.

A cast-off from the screen-printing industry is a better option if you're serious.  I managed to rescue an old and rusting UV printing frame a few years ago, rebuilt it, and it now serves as a very useful light source together with having a vacuum facility to ensure that negative and print are held in tight contact throughout the exposure.