What they don't tell you about an ALPS printing in white, is that it is used as either a spot color - or - a background color only.
The top of the line MD-5000 is rated at 2400dpi which is awesome, but that is for the CMYK primary inks only. White, being a spot or background color will only do 600dpi.
The thing about a color printer, is that on your computer monitor, the white you have in your artwork was intended to go onto a sheet of white paper (like any typical home or office printer). Therefore - what happens? Since the paper is white - the computer sends a no-ink signal for the white areas. When you print onto clear decal paper using an ALPS, the same thing occurs. The white on your artwork does not "tell" the white ink cartridge to print white. You end up with clear areas where the white is supposed to be.
Using spot color mode, the ALPS will make a pass with the white ink, but it's merely doing a white version of the regualr colors, and mostly in their location. Plus it's 600dpi next to 2400dpi colors and black. SO... white in spot color mode is essentially a thin white layer, a little fuzzier, behind your other colors.
Using background mode... the ALPS will run a solid silhouette of your images (heralds, text lettering, whatever is on the page) in pure white as a base color. (You know those people interviewed on TV who want to hide their identity - and show up as a black shadow of themselves? Well... this would be in white). Then you run the CMYK layers over that. At least NOW your white areas show up white on the sheet. But, here again, the white prints 600dpi and the colors go on 2400dpi. (Yes you can make the colors print 600dpi also, but then you don't get to use V-photo mode which is what you want). So now you have a halo white glow around your color images and even worse, your black lettering! And - depending on how many images you cram onto a sheet - that is a LOT of white ink being used!
A remedy some have tried, is to take a white cartridge and put the label bar code from a black cartridge on it. To fool the ALPS into thinking it's a black cartridge. I won't go into real detail, but the ALPS works by shuffling each ink cartridge internally, finding them by scanning the bar code labels. So... if you have a fake black cartridge (which has white ink)... you simply have the computer do black lettering, and it comes out white, but in the sharper 2400dpi. As the bar code labels are metallic tape, you have to be careful removing them and so forth.
Myself, I now just run my full color stuff on one sheet, and my single color lettering on a separate sheet. That way I use the white background on the full color images, but not on my black lettering. The urge to conserve decal paper originally had me cramming image after image on an 8.5 x 11 sheet... but after my crisp black road names came out with a thin white outline, I went the separate route.
Which brings us to printing white lettering and numbers. Without doing the label swapping - you pretty much run your sheet of black lettering and numbers - starting with a white background layer. Then re run the white background layer, and cancel out the rest of the color passes that would have followed. White lettering but in 600dpi, which will pass for HO and N road numbers and initials.... but not tiny data such as weight limits and build dates. Plus the ALPS printed white lettering will not be as sharp as pad printed factory lettering, such as that on a new freight car body.
Mike