Water Surface Tension

Water Surface Tension
Although its been a lean month for ‘Cog’ developments, due to paid work and the desire to step back and recharge my batteries, I have done some experimentation into surface tension on water. It has always bugged me when I see objects in CG water with no reaction i.e. surface tension. Tiny details like that can help create reality no matter what style the image or animation is rendered in. Whereas if these small details are missing even the best photo-reality render will be unconvincing.

The above image and the associated movies on my site were produced using the inbuilt procedural textures and raytrace renderer. The surface tension effect is a blurred white rectangle mapped to the pilling object and added as a displacement map. Adjusting the amount of displacement, and varying the size in the mapto panel, to produce just the right amount of surface tension effect. The image needs to be quite large (mine is 2048 x 2048) to give a gradual curl up the sides of the pilling. If the image were too small it would produce a step like effect, because the pixels would be too large.

Visit www.cogfilms.com where you will find two animations with the effect in motion.

For those who prefer direct links:-

water-surface-tension-cyclic_640x360.mov (QT 2.2Mb)

water-surface-tension-cyclic_320x180.mov (QT 1.1Mb)



shouldn’t this be in wip or finnished projects?

[nice job making it shiny…]

Fancy… I always (two times, hehe…) did it with geometry.

Nice, must have a go at this method.

I presume for a complex scene with many support posts for a pier, you could render a top view to create the neccesary image file for the bump?

I just can’t see how you could have a new white texture for each post, if each has to be mapped to that relevant post. Unless I’m mistaken and you would have multiple materials for the water.

Very good method none the less.


Hi Z3r0 d

Neither, as this is an explanation, tutorial, small bit of help to other users, and that’s what the general forum is so good for. Although I guess all work is in progress :-?


Hi sonix,

Yes I have used that technique before, remembering to set the camera to orthographic so that there is no perspective distortion.

Depends how many posts are in shot. With 10 texture slots you could have 9 plus the wave texture. The important point is that the surface tension image should be large to avoid pixilation ruining the effect.

This is a detail of the map used (2048x2048)


and this


is the same image but (512 x512) which as a displacement map would produce a stepped effect.

Thanks very much.


Hi Trident

I feel somewhat of an idiot as I did use displacement rather than normal mapping. I must remember to get more sleep.

I have amended the first post and my website. Your comment made me think and check and discover my error.


Thank you for seeng some sence in just a “me too” remark :slight_smile: As for ways to create ST… I’m currently trying to do a tea in a cup. Studying it, drinking it, tweaking model… Hey, never thought that surface of tea is so complex and hard to reproduce… But well, i’m a n00b. :slight_smile:

(Accidentally submittetd in the middle of posting. )

Well for this type of scene geometry IMO is still better than textures, there are bubbles right there anyway. :slight_smile:

do you think you could go into a little more detail describing the process you went through to create that? also, what are your water texture settings? they look really good.

Hello SkeLeToR,

I think I will have to create another ‘Cog’s Quick Tutorials’. Apart from the surface tension there are other things in the concept such as the water texture and also the wooden post. I have also done a little painting with light to help bring out the surface tension.

Anyway I will create another tutorial during May and post here when its on my website.


Hi Cog, I just wanted to say I visit your website everytime it’s updated, and I always look forward to new info on the Cog movie, and now I am looking forward to your new tutorial

Thanks Squirrel,

It’s always good to know that ones efforts are appreciated.


ooo please do post the tutorial soon even just a basic work flow with out images would be cool and helpful

Oct 2005

Cog’s Quick Tutorials #3 Water Surface Tension in Blender now published.