As there were some questions raised in this topic I thought I'd compile a little guide for using Dylon to dye puzzle parts. (Actually I wrote this post a while ago but only just got around to posting it)
Nowadays Shapeways offers WSF dyed black as BSF so this is not as important as it used to be, but dying on your own can save you a lot of money ($20-$50 per puzzle, which adds up when you dye 5 puzzles at once).

Personally I use Dylon (the kind that comes in tins, it is called Dylon #8 Ebony Black) but other forum members use RIT fabric dye. I will outline the process for Dylon, the process when using RIT should be about the same. Always follow the instructions specific to your dye, especially the safety warning. Both of these products are designed to dye clothes so they give nasty stains (not only in your clothes but also in some kitchenwares and counter tops) so be careful! You can Dylon and RIT at some drug stores and tailor shops.

1) Clean the parts: fill a pot with enough water and bring to the boil. Boil the parts in the water for a few minutes, then add dish soap and boil for a little longer (be careful not to let if foam up). Rinse the parts and your pot very well before continuing to remove any trace of soap.
2) Prepare the dye: bring enough water to the boil to cover the parts. Add the dye to the water and stir to dissolve. In the case of Dylon, add 20 grams of salt for each packet of dye.
3) Now carefully add the parts to the dye and boil them in the dye solution for about 20 minutes. Take great care not to let it boil over or you'll have a very big mess to clean up! Stir often to make sure the parts dye evenly
4) Dump the contents of your pot in to a sieve and let the dye flow down the drain, then rinse the parts with copious amounts of water to remove leftover dye. Shake off excess water and let the parts dry.

I find that the best results are obtained if you break in the puzzle prior to dying. However you should not sand the puzzle because sanded areas do not take the dye well. Also sanding after dying is not a good idea because the dyed layer will only be very thin.

To obtain a nice, deep black:
- Boil vigorously all the time, don't just simmer
- Make sure the dye is nice and concentrated. For best results, use one container of Dylon for at most 3 puzzles. You can get away with a 4:1 ratio but you should really add in another packet of dye when you get to 5 puzzles. Also, don't dilute the dye by adding more water than necessary (you still want the parts to be well covered). I think RIT comes in much larger packets so this does not apply to RIT.
- You can touch up your puzzle with a black permanent marker. Just coloring the edges of the pieces (stickers cover most of it and the inside does not matter as much) gives you a puzzle that looks much nicer. The marker really gives you a deep, deep black. You will need to play with the puzzle for a while to allow all the excess ink to come of on to your hands, just use some hand soap and it will wash right off.

Thanks for this Tom. One thing which has always caused me problems with dying (well, the once I dyed a puzzle anyway) was when washing the parts. My parents seem to think that when pouring the dye down the sink it will stain the sink or stain minor scratches in the sink. Can anyone tell me if this is true? Last time I had to do labouriously do it at 9 o'clock at night in a bucket with a hose, then walk about 50 metres outside my property where I then through the dye out from the bucket.

Yes, it does make your sink black but it comes right off with chlorine. My sink is a stainless steel one.

Thanks for that Tom. Now to make a mess ...

Thanks Tom! This will come in very handy.

Carl

Hey this got me wondering... Is Shapeways dyeing process similiar to ours? I would think they could start off with a powder which had been dyed black and produces a puzzle which was black throughout. I.e. you could sand it and not expose a white surface. Not sure if that is how they do it or not. Anyone know?

Carl

Well, this is true, but you were talking about dyeing, right?