The printing process leaves a waxy, oily residue on the models, and needs to be removed. I soak my models in a jar of solvent overnight. I use Bestine brand which was recommended on multiple online forums, and works very well. I have found that the solvent won't hurt the models even if left soaking for several days. In addition, if you are in a hurry, the solvent seems to work fairly well in a short hour or less. After soaking, I rinse the models with regular water and lightly scrub with an old toothbrush. After the models are dry, they will look like white styrene. There may still be some left over residue on the models and I remove this with files, sanding sticks, and other cleaning tools. I have purchased several dozen models to date, and most of them only required very minor clean up before painting.
I then spray a couple coats of white primer. I simply use a can of Rustoleum for this job. The printing process leaves some minor texture in spots on some of the models, and I have found that a couple extra coats of primer will help smooth out these surfaces and provide a perfect finish after the color is painted.
I use common techniques for the painting process, and use both my airbrush and a hand brush for details. Polly S and Model Master acrylics have worked well for me. I recently discovered Vallejo paints at my local Hobby Lobby and picked up a few bottles. This particular line of paint is meant for brushes, but they do also carry a line specifically for airbrushes. A good example of this paint is the yellow Showcase Miniatures Kenworth T600 which was completely hand painted using Vallejo. The red simulated tarp on my 43' Wilson grain trailer was also painted using a brush, and leaves virtually no brush marks at all.
For now, the new layout is my working surface for all of my 3d printing projects. As you can see, I have a lot going on. You can see the solvent I use, and the jar with a couple models soaking.
Here is a good example of the various finishing steps. The flatbed is right out of the package and has the oily/waxy residue on it still. The bottom dump trailer is dry after soaking in solvent. The Pete cabs and frames have been sprayed with white primer. You can also see how I group my wheels on a sprue.
Here is another example of my Pete with white primer, a coat of blue Model Master before adding the grill, air filters, and paint details. And finally a completed model in orange.
Here is a 43' Wilson grain trailer with simulated tarp, and a 50' version with spread axle. Both have been soaked in solvent and are now dry and ready for primer. These are very clean models and will require very little clean up.
Here is a pair of Kenworth T800 cabs and frames just out of solvent and waiting for primer. You can see the suspension detail in this photo.
The bottom dump trailers are great models right out of the solvent. They require very little clean up. This is an example of a model where I apply a couple extra coats of primer to the sides. The printing process leaves very minor horizontal line texture which can be lightly sanded, and primed to provide a perfect smooth finish.
There you have it. Some good examples of my models, and the steps to get you started in finishing them. As always, I am very interested in your feedback and hope you have success with your own models. My Shapeways shop has many models to choose from currently, and I hope to add more in the future: