The chemicals are a lot safer than what is under the kitchen sink or in the laundry room (or, heaven forbid, the garden shed [even worse, the garage]).
+1. But that said, even apparently innocuous chemicals can cause some harm when proper care is not taken. I don't know how many photographers have had chemistry experience, but I guess they number in the low percentages. I am a chemical engineer, and have worked with pretty dangerous stuff far worse than household chemicals. But I still respect those household chemicals, as do I the chemicals in my darkroom. It is always a good idea to get some guidance before going solo.
Various countries have different legislation regarding chemicals, and shipping and importing them also differ somewhat from country to country. While most chemicals are available from US photographic suppliers to US customers, many of those chemicals can't be shipped outside of the US, and other ways must be found to source them. There are very few photographic chemicals that are not used as feed material or ingredient somewhere else in industry. I was stunned the other day to find sodium thiosulphate (hypo) in 5 kg packaging in my local farmers supply and hardware store. It is used as a food additive for cattle, apparently. Still looking for ammonium thiosulphate, though. Phenidone is used in hair products, as is amidol. But I am not sure that metol has any other uses. A supplier of bulk and/or fine chemicals such as Sigma Aldrich or Merck will have just about all the chemicals you may need on their list. If you can find a chemical or repackaging plant in your vicinity that buys bulk quantities and they are willing to spare you a few hundred grams of something, you can get very far with that. I got 100 grams of phenidone for free, and it will last me another few decades.
The easiest concentrate to make, in terms of number and difficulty of steps, and in terms of sourcing and handling the necessary chemicals, is Parodinal. It requires four chemicals: Paracetamol (pain killers), sodium or potassium sulphite or metabisulphite, sodium or potassium hydroxide and dihydrogen oxide, otherwise known as water. I was able to acquire 2.5 kg of paracetamol from a bulk supplier, but needed a friend with a pharmaceutical license to order for me. It cost ZAR 215, or approximately 18 EU. It is enough to make 33 liters of concentrate, i.e. to develop ca 3300 films. Potassium metabisulphite is used as food additive and in winemaking etc, so is very easy to obtain by the bucketloads. Sodium hydroxide is commonly sold in grocery and hardware stores as drain cleaner. All you need apart from the chemicals is a scale that is accurate enough, and glassware to mix it in. I make anywhere from 200 ml to 1 l at a time, and do the mixing in Erlenmeyer flasks as those are easy to swirl and heat for dissolving the chemicals. Paracetamol does not dissolve in water easily, but does dissolve in a warm hydroxide solution. So I add the hydroxide to water and let it dissolve, then add the paracetamol to that solution. I dissolve the sulphite or metabisulphite in another flask, then I combine the two parts and make up the final volume with water. The whole process of weighing and mixing takes all of about 10-15 minutes, and only that long because I don't rush anything. After standing for three days, the developer is ready, and will last many years on a shelf.
Sermon: Of course 10 grams of paracetamol can be a lethal dose, and hydroxide will burn skin and eyes, not to speak of the intestines if you care to ingest it. The rule is to store these things away from vulnerable people e.g. children, and to wear PPE during handling. Clearly label everything that you repackage, including the developer itself. That way your kin will know what to do with each item if you succumb in a plane crash or something. It is not a nice job to clean up a warehouse full of unlabeled and potentially fatal chemicals, and it can be very expensive to characterise and dispose of chemical waste. Buy and store only as much as you think you will need for a reasonable time. Think about what you leave behind and how it has to be dealt with in your potential absence. End of sermon.
Have fun
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Confusing this chemistry stuff.
