How to prepare an object for scanning

[WalterMo]

Sometimes it's necessary to prepare the surface of an object to make it scanable.

So let me open a new thread where users can share their experience of their used method. The layer, a powder or a paint or whatever should be removable and not damage the surface of the object.

To have an objective comparison we need something like a standard, e.g. a coin which should be shown on the same photo with and without the layer.
Let me begin with chalk spray used by me to prepare the backside of my car some days ago. It's very good shielding, cheap and rinseable with water.
Sprayed on cloth it can be removed with a brush mounted at the hose of a vacuum cleaner.

And it is very environmentally save.

Walter

Edit:
Now after a carefully „inspection“ of my car I must realize that some plastic parts have changed their surface a bit. Not all but some are matt.
For example: To protect the paint when goods are loaded through the back door I had glued a transparent foil at that part of the car (bumper). But now the transparency isn't the former one. It's a bit matt. That means care should be taken when the chalk spray is used on plastics.
Perhaps I had let the chalk too long on the car? The time was three or four days.
I think the chalk isn't the problem but perhaps the binder.

[bartjuan]

Walter:

Would you be so kind as to list the manufacturer and/or brand of your chalk spray. I am not familiar with the product.
I assume it must be available at a hardware store or craft store. is this true.

Thanks for this thread.

Bart

[WalterMo]

I bought the 500ml bottle from a German online shop specialized for painter requirements. They are writing the content would be enough for 2.5 square meters.
The spray itself was produced by Dupli-Color. The heading was multilingual:

Kreidespray
Marquage à la craie
Markierungs Spray
a base di gesso
Whiting Spray

Walter

Edit: In the meantime you can get chalk spray from the DAVID shop. It's called there „Kreidespray“: https://ssl.david-vision-systems.de/sho ... y/Zubehoer

[hal]

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 (*);
- Glass;
- 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 ,
Mattia

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.

[florin.topala]

BRAVOO & tx for sharring

[hal]

Hello,

in according to WalterMo's suggestion, I've applied the "soapy" coating on a metal, polished and shiny surface of 2 € coin.
Sorry for the scan, isn't good but this is only a test to prove the coating method, so the calibration was done at fly, quickly and imprecise.

Best regards,
Mattia

[Bongobat]

Hi Mattia,

Great idea!

I recently purchased an airbrush http://www.harborfreight.com/cpi/ctaf/d ... mber=95810 and I was wondering what the ratio of water soap and tempera paint you use? Also it looks like you are getting a very fine coating that preserves the detail. Do you think tempera is better than a good acrylic. I know acrylic is permenant but for what I want to do right now it is more important to be a thin coat rather than temporary but I looks like tempera may be a better solution.

thanks,

Greg

[hal]

Hi Greg,

sure that an acrylic colour is better than a tempera colour: more covering and uniform to spread.
If your purpose is to have a good and bright coating, the acrylic color is the right choise.
About tempera and the ratio of water and soap, I think that all is related with your tools: if you use a soft brush is better a dense color (- water + tempera), but for your airbrush is better a more liquid color. I can't suggest a determinated proportion, but I think that isn't so important to saturate the water with the soap, especially if you use an "agressive" soap, like a soap for dishes.

First of all, try with few drops of liquid soap and spread a layer of colour on your surface: if the surface tension is decrease and the colour stick perfectly, you have the right ratio of soap and water.

Bye,
Mattia

EDIT: I've cleaned, only now, the Lamborghini scaled model ( viewtopic.php?f=7&t=790&p=4555&hilit=lamborghini#p4555 ) coated, time ago (November 2008), with only water colour tempera. I've used an airbrush to coat the car model, so, there was many layers on its metal/plastic surface. The main problem was that many layer = exfoliation and loss of color in many areas. Now with soap we can avoid these problems.
But the important news is that tempera can be removed completely and without any problems even after many months. The aged tempera isn't a real problem for our meta and plastic surfaces.
Bye, Mattia

[MagWeb]

Hi,

just tested FROTTEE dry shampoo spray. Gives a very easy to remove thin coating (simply to be brushed away).
Gives not a complete white, but mate and much brighter surface.

Just another possibility - should be usefull for scanning human heads....

Gunter

[RAYA]

Hi Mattia

Thank you to share your formula

I want to add DEGREASING which can lower the surface tesion before to covering or painting.

Did you test soaking ?

Ray

[hal]

Hello,

I've find an other product to coat our object, for scanning.
We can use the CYCLODODECANE SPRAY. It is a common product in Art Restoration.
I've attached here below the Technical Report (one is in English, one in Italian and other in German).

The spray allow a thin white layer on a lot of kinds of surfaces. You can remove it easily with a dry brush, White Spirit and (this is the cooler thing) only waiting!
Yes, the product sublimate itself! The time needed for sublimation are in relation with the enviromental temperature and with the thickness of your layer (How much have you sprayed). Usually for thin layers the product sublimate in 2 days. If you want to accelerate the sublimation, you can use a warm breath of air (e.g.: an hairdryer).
This can be useful on delicate object and on not-washable surfaces (paper, clothes, ...).

Mattia
Hope that can interest you,

[MagWeb]

Hi Mattia,

I already heard that such a spray exists, but never found it - thanks!

This is interesting stuff but seems to be also dangerous F+ (highly flameable). In Germany its use is restricted by law only for professional use and you´ve to declare and document its use at the authorities.
The problem seem to be that the spray uses a mix out of butan and propan.

Cyclododecan instead seems to be not as dangerous and you can get it without problems. Can one use this - maybe using another technic to apply ?

Gunter

[hal]

Hi Gunter,

sure, you can buy the Cyclododecan as solid product and after melt it and mix with White Spirit or Petroleum Essential Oil.
After, you can spray it with an airbrush.
Here in Italy the only advice for safety is to use a mask. Keep in mind that this product is usually used into a yard, in laboratory and especially for archeological restoration. Probably the German people pay more attention to the health (I think that we have many things to learn from German people, and not only in this field of knowledge).

Mattia

[MagWeb]

Hi again,

Please don´t learn too much ... sometimes these classifications are a bit bureaucratic...

At Kremer Pigments I found also Menthol and Tricyclen-Campen (technical mixture) as similar vanishing substances. Menthol is a bit expensive. Don´t find whether Tricylen-Campen gives a visible coating - do you know (it would be cheaper than Cyclododecan)?

Gunter

[santo]

Hello

For the digitalization of the brilliant or transparent objects, I use a solution containing titanium dioxide. This titanium dioxide (White of titanium) reverberator particularly well the visible light, and, especially, the wavelength of the red lasers. The aqueous solution is water mixed with ethanol, and a saponifying product (liquid crockery). Alcohol and the liquid crockery are used for lowering the surface tension and, thus, making it possible " to wet " materials such as the plastic or metal. I pass this solution to the brush, after drying it is possible to remove this coating. The question which is not solved, it is that in the case of a digitalization with texture, it is necessary to clean the object with each scan, to take a stereotype,
and to give the coating, and quite sour it is difficult to give the object in the situation of the scan. I think that the solution would reside in the possibility of making the stereotypes of texture after the totality of the scans, but that supposes to precisely find all the positions in which summers have made the scans.
Does somebody consider another possibility?

In a friendly way,

Pierre