Surface differences with Frosted Ultra Detail

Hello everybody,

i was wondering if anybody can explain to me why there are differences in the looks/the surface of FUD models.
To explain what i mean please take a look at the first two attached pictures. As you can see there, there are areas of the model that are almost completely transparent and some others areas are frosted.

This is important to me because i clean and finish them by using Isopropanol. This has the nice side effect, that it turns the matrerial to a nice white finish and makes the surface a little porous, which can be painted very well. For examples of finished models please take a look at the third and fourth attached picture.
This nice side effect however occurs much better on the frosted areas and not so well on the transparent areas. On the transparent areas, after treating them in the described way, i get at best only blurry results. See the fifth picture.


I assume that it might depend if the surface is flat or bended, but as i said, i hope maybe can explain it to me. In addition to an explanation it would also nice to know if i can influence the frosted effect on the model somehow, so that my model has no clear areas but only frosted ones and so that i get a nice and evenly finish.


Thanks for your answers and kind regards,
Christian

Wherever the support material touches your model it will have that frosty appearance. The areas that the support material is not needed come out looking smooth and translucent. You may be able to have your entire model embedded in support material by placing a cage around the entire model. The cage will need to be support as it is printed so your model, which is inside, would need to have support material built on top of it.

It's not the same material, but this image gives one an idea of how the support material is used.
The light colored areas make up the support material.

Thanks for the fast reply.
Ok, so it is about the support material, good to know.
I do understand what you mean with building a kind of cage around the model that i want to be completly covered in the support
material. However that would only work if Shapeways prints the file exactly like i send it to them. Does anybody know if this is the case or if they feel free, in order to optimize the printing process, to mix files and orientate single models in the most efficient way?

One other though about building a cage would be, that the cage of course requires material what will increase the price for the print. And with FUD this can be significant...
Could it be, in order to avoid this, a solution to build the cage out of other models? I attached a file to show what i mean. However this again would require that Shapeways prints the file exactly as i send it to them...

Several people have been recommending heptane (trademark "Bestine") for cleaning FUD over in the Post Production Techniques forum, and the images that accompanied their recommendation appear to show uniformly white "frosted" items - so maybe some chemical attack on the acrylic material is involved, and your isopropanole is just too polar for maximum effect ?

Yes, Shapeways does load the machines in a manner that is as efficient as possible for the print run. Orientation would not matter though in this case if your model were completely encased in a cage. And yes, it would add to the total cost quite a bit.

In addition to a chemical treatment as suggested by mkroeker, perhaps one could get a similar effect by doing sand blasting with a very fine grit; around 220 grit or so for example.

Thanks again for the answers.

I think i will try different ways of chemical treatment. The models i let print are for 28mm tabletop games and therefor have regulary very small surface details. I fear sand blasting, even if only with a very fine grit, will result in the loss of some of the details.

Right know i am testing lighter fluid and spiritus. Tomorow i will test white spirit.
In regards to heptane, i will try this as well, but because i live in Germany Bestine is not an option for me. It´s not sold here and ordering it from the USA seems to be not possible due to flight safety regulations. I still have to figure out where to get some heptane here...

I will post some of the results of different chemical treatment once i am ready with testing.

"Waschbenzin" should be close enough for the purpose, or try a pharmacy (it's been years - decades actually, since I last had to buy any "chemicals" there, so no idea if regulations or attitude has changed - if they cannot or will not sell you heptane, ask for "Wundbenzin")