Hello and many Thanks to WalterMo
for this topic.
I want to show a simple method to coat our "hard" surfaces without any risk to damage they, easy to do and easy to remove.
Probably many of you already knows a better system to prepare the surface of an object to scan, but if you haven't a better solution, try this.
First of all, what surfaces are so problematic or impossible to scan without a coating?
Some object considerated hard to scan are:
- Plastic shiny surfaces (*);
- Plastic surfaces with Sub Surface Scattering (*);
- Plastic surfaces trasparent (*);
- Metal shiny surfaces;
- Skin (**).
The best way to coat something with a color (mixed with a medium like the water) is an airbrush or a spray, but we can achieve good results with a simple brush.
A well know material for coating is the white talcum, but its layer is very thin and very easy to remove (with a sneeze or an accidental touch). So we need a colour to mix with a medium and easy to remove: water color (tempera) is a good choise and easy to find in any paint shop and very cheap.
Time ago I tried to coat some plastic toys (shiny and semi-opaque surface) with a white water colour (tempera colour). As you can imagine, the water can't stick on the plastic, glass and metal. The drops of the water slide away. So, is hard to fix a colour mixed with water on these surfaces
The problem of this water color is the surface tension of every water drop ( http://en.wikipedia.org/wiki/Surface_tension
BUT if we reduce this surface tension, we can spread better our tempera colour on the "hard" surfaces.
For this purpose we can use the soap
(yes, the same soap used for wash our hands). We must simply dissolve some soap into the water and add the colour. Now the surface tension is drastically decreased and our drops of water + color should be spread uniformly on the entire surface.
But some images are better then many words.
In this first image you can see the difference between a simply tempera mixed only with water and tempera mixed with water "saturated" with soap.
As you clearly see the colour on the left leg (from your point of view) isn't usefull for a good scan process for this semi-trasparent and shiny toy. The right leg, instead, have a quite good and opaque layer of colour.
On the glass the result is the same.
With only water is impossible to have a uniform and good coating with tempera, but with some soap we can have a good layer of opaque colour.
Finally a comparison with the most used coating system: talcum.
Talcum can coat nicely our surfaces, but if they are shiny and polished is hard to keep it on the surface. And if we can coat with talcum is hard to handle the coated object without remove the talcum layer. So I think that tempera + soap can be a good compromise with easiness of use and reversibility.
In the image below you can see the difference of coating.
Please pay attention to use the tempera on un-washable surfaces and precious object.
I hope that this quick test with water color and soap can be useful for your purpose.
Best regards to all and good coating
p.s.: I've added the low resolution 3D model, as .pdf file, here: http://www.david-laserscanner.com/wiki/ ... ia_gallery
, and some images here: viewtopic.php?f=7&t=681&start=30
.(*): remember to wash away the tempera color from your surfaces in the same day that you coat the object (or don't leave for many time the coating on the surfaces). The tempera color can stain your plastic surfaces, especially if they are just a little porous, if you leave the coating for a long period on the object (more than two/three days, especially if your room/envirorment is warm).
(**): you can use the water color on your skin but with carefully. Pay attention to don't use tempera on delicated areas of your body (eyes, nose, mouth, genitals, ... ), don't eat it and wash the coated skin just after the scans. Obviously for scanning of people and living object is better a dedicated body colour.