How would you light black water?

[Big Mike]

It appears that ferrofluid is characterized by direct reflection (and absorption, it is black). Part of that may be polarized reflection, so you might try a polarizing filter, just to see if it makes a difference.

So because you are dealing with direct reflection, the only parts of it that will be lit (seen) are where your light source is directly reflected, and the parts where you light source isn't directly reflected, will be dark.

As such, you need to think about your family of angles. That is the angle from the camera, bouncing off the subject and to the light source. The problem with that, is that if you give it shape & form, you angles will then be all over, so your light source will show up. Therefore, the shape and relative size (& proximity) will make a difference in the lit areas of the fluid.

As mentioned, it may be a good idea to have a rather larger light source, so that you fill more of the angles, and thus light up the fluid more. Many of the example photos that I just looked up, had a large light source behind the fluid, which fills the family of angles from the camera position, on any parts of the fluid that is flat.

It doesn't need to be a softbox etc. you could point your flash at a wall, to create a large light source. The key point will be the size & shape of the light source, because that will be directly reflected by the material.

 

[c.cloudwalker]

I have looked at a few videos on YouTube and the lighting is not very good in most of them.

I think I would shoot this same way as I shoot cars. With a softbox that is larger than the dish in which you keep the fluid on top. Then a softbox on each side, again, larger than the container. Then you'll have to play around to get the lighting ratio that gives the best image or, should I say, the image you want.

Basically, when shooting highly reflective surfaces, you want a light source which is larger than the object you are shooting. This way the reflection covers it entirely and it's not annoying anymore.

The biggest problem I noticed in the videos is that the dish/container is always part of the image and it's not very pretty but, at the very least you could pick a container that is not reflective.

 

[flyingember]

ferrofluid! I need some of that stuff.

With black water I instantly thought of this photo. you couldn't see anything more than a foot down.

Waiting Over Black Waters | Flickr - Photo Sharing!
I took this on a cheap disposable waterproof point and shoot 6.5 years ago. the spots were water drops, I was soaked too at the time so there was nothing to clean the lens with.

 

[Overread]

Many thanks for those pointers - I've been considering those viewpoints as well as looking at some shots myself - it seems that the trick might be more to work with the reflection than against it - but I'm still determined to keep trying alternate setups.:

An early shot stack:

http://farm6.static.flickr.com/5089/5265942476_a26560025a_b.jpg

Stacking also hasn't worked 100% with this shot (you can see an error on the far right spike) however its mostly managed to get the stack correct. This clearly means that any stack series ideally wants to have more shots and also maybe even a repeat before committing to the software - to help ensure that at least one stack works.