Hi Gary
I recently set myself the task of taking the best pictures I could of several of my pipes. I took a while, sometimes 25 mins to get one good exposure, although I am used to Street Photography, so this was a foray into a different discipline for me. But I echo the advice to use as much light as you can. I waited until noon on a sunny day and setup a couple of boxes on my wide windowsill then draped a plain T-shirt over them. The camera used for most of my album pictures was a Canon Eos M1, using spot metering, low iSo and apertures of around f/6.3. Then it was a case of using exp. comp to capture the best balance of detail and 'zing'. In my most recent photograph of my Pete 106, exposing correctly just didn't seem to work. I think I dialled in about -1.3 E.V. which is very unusual. Of course, when selling, the most important thing is not to blow your highlights and to rest your camera on something to take a clear shot, photographing every part of the pipe in the same conditions. It can be tricky but the rewards are high. Just look at eBay- a good photograph can boost the price of an item considerably.