I have done steam before, and it is not an easy matter.
First you have to understand how light reflects off of water vapor. Second is understanding the contrast of water against light or dark background, and third is to set up the shot with either a fast or slow shutter.
Each variable is different.
Back lighting will give off a shadow, or darker vapor because the light is coming from behind the water. You will not see it very well with a dark background.
Front lighting, but directed at the vapor itself with a dark background some distance away will cause the light to reflect off of the vapor giving a white or light appearance, but will be unseen if the background is light in color.
Angle of the camera is critical here…
Third is the shutter. If the shutter is set fast, you will get vapor detail, and the image will appear a bit grainy.
If the shutter is slow, you will get the smooth flowing feel, but lighting is critical.
A digital with adjustable features works well here, and you will have to experiment.
Believe it or not, the harder the water content, the hotter you have to get the water witch will result in more vapor. Softer water will vapor out at lower temps…(by only a 1 or 2 degree difference) but will result in less vapor.
Use a ceramic cup, given that the ceramic will hold the heat longer. A solid tripod is a must on this one, along with consistent lighting.
In 1992 it took me 30 tries, and about $80 in film to get the shot right. The photo and negative was later lost to a certain incident. So don’t give up…