File names which end with ".bmp", ".tif", ".gif" or ".jpg" are bitmapped images and can be opened with most computer graphics or photo-editing software. You can then alter or modify the files, but be careful when enlarging. The "dots per inch" (dpi) of the final printed image is inversely proportional to the magnification. Pictures with less than 100 dpi begin to look fuzzy and indistinct, as the dots of ink are stretched farther apart from each other.

You cannot alter or modify PDF files with the Acrobat Reader, though you can open them with the Adobe Acrobat creator software, or the most recent versions of Adobe Photoshop and Corel Draw. One way to transfer Acrobat images to a graphics or photo-editing program is to take screenshots and then import your selection from the clipboard. You will also be converting it to a bitmapped picture, so you should first enlarge the Acrobat file to the desired magnification. Some "cut and paste" work may be required for pictures too large for a single screenshot.

Inkjet printers with a high resolution (600-740 dpi and up) are perfectly acceptable. Choose a printer that uses four colors: cyan, magenta, yellow and black (CMYK). The cheapest inkjets only use three colors, so "black" is really a dark purple-brown.

Color laser printers produce sharp images and a smooth surface, but they are expensive and most do not have a straight paper path. Sharp creases may cause laser printed images to crack, exposing the white paper. Careful folding can prevent this from occurring, or a little touch-up work may be required.

The ALPS line of computer printers deserves special mention. These printers use a dry thermal film process, producing fade-resistant and waterproof prints, metallic effects and even white images. For these reasons, some plastic modelers are using ALPS printers to produce custom decal sheets. However, there are certain considerations when printing card models. Print speeds are very slow as the paper goes back and forth multiple times. The ALPS film cartridges can be expensive, and glue may not bond well to the waxy surface. Also, the print head slightly overlaps on each pass, so there is a noticeable "banding" effect on large images. Since the color films are heat-bonded to the paper’s surface in multiple layers, scoring, rolling or sharply creasing the paper will cause the film layer to crack. Flaking or delamination of the color layers may then occur. Dye-sublimation printers are similar to ALPS printers, so the same warnings apply.

Brightness is another factor when deciding which paper to use. This is a measurement on the opaqueness and "whiteness" of the paper. Most copier paper rates an 87, though inkjet and laser printer sheets are 92. There is a noticeable difference in color vividness and contrast between these two grades, so look for a high brightness number.

Finish is also important. Paper can have many different textures, depending on the rollers used during the manufacturing process. Some sheets have a smooth surface on one side only, which should be used for printing. The less finished side will have enough "teeth" for secure gluing. Paper that is too absorbent will soak up inkjet colors, leaving a dull, blurry image. In addition, they will be more vulnerable to sagging as humidity changes. (Some otherwise excellent models from Poland are printed on extremely coarse paper, which modelers derisively describe as "burlap".) Other varieties of paper may be lightly coated with special kaolin clays to reduce ink absorption; these papers also tend to have higher brightness ratings.

Avoid glossy (and expensive) photo quality paper for printing paper models, as the inks are more vulnerable to smearing. Glue will have difficulty adhering to the slick surface, and clear sprays may bead like rain on a waxed car. Also, don’t spray any finish on a sheet of paper before running it through the printer. You risk paper curling, ink smears and printer jams.

Cardboard 1 mm and thicker is oftentimes used for interior reinforcement or structural support. For these pieces, a pattern is laminated onto the cardboard prior to cutting. If the thickness isn’t specified in the instructions, you can usually deduce it by checking the width of the slots. You might want to ask your local framing store for scrap matboard pieces, especially if the kit requires a specific thickness.

Since acids are used to break down wood fibers during the papermaking process, most paper will slowly self-destruct. (It is the acid content, not necessarily sunlight, which causes newspapers to yellow and become brittle.) To extend the life of your paper model, look for "acid-free" or "ph-neutral" stock. This will not protect your model from any acids in the inks, sprays, adhesives, or the sweat on your hands, but the aim is to keep any acid exposure to a minimum.

I spray the printed sheets with gloss sealer so I can carefully clean up any white glue spots with a damp cloth during construction. Also, CA (cyanoacrylate adhesive) darkens unprotected paper, and leaves a white "frost" on matte-sprayed surfaces when it cures. Gloss surfaces tend to resist such reactions from CA. I usually spray the completed model with gloss to blend in areas shiny from CA, and then apply a light dusting of matte after the first coat dries completely. Don’t be concerned if the gloss spray looks slightly "speckled", as this will disappear with the final matt coat. However, runs and drips should be avoided.

I used Testors Glosscote and Dullcote sprays (a legacy from my plastic modeling days), but the small 3 oz. cans are not very economical. Presently, I am experimenting with Krylon products. Krylon UV-Resistant Clear is a gloss that protects against sun damage. Be careful about Krylon Low-Odor Clear Gloss. While this latex acrylic spray produces less hazardous fumes, it causes the paper to curl and warp. It is also prone to beading. There are other artist fixatives and spray varnishes that should work fine and are available in hobby, arts and craft stores. Personally, I had no problems using lacquer-based sprays (except for the smell), but tightening air-quality regulations and health concerns have caused paint manufacturers to reformulate their products. Regular acrylic finishes are satisfactory, except that paper has a slight tendency to shrink and curl. A light spraying on the other side may counteract the curling, but make sure the printed side is completely dry first. Some acrylic sprays contain isopropyl alcohol, so the ink is prone to smearing until the sealant cures.

When spraying, multiple light coats are mandatory. A heavy, soaking coat of clearcoat may cause paper to curl, become translucent, or lead to ink bleeding. Also, some paper may completely absorb the finish during the first spraying. A second (or even a third) coat may be needed after the first dries.

If the model is sufficiently protected with lacquer clear coats, you can touch-up spots with paint, or add weathering with powdered pastels. Even light airbrushing is possible. Some paper modelers have installed motors and radio control units in large, heavily-varnished ship models and actually sail them with no ill effects. (Hopefully the glue is also water-resistant!)

Cyanoacrylate adhesive (CA) is not suited for gluing paper. "Superglue" is useful for attaching other materials, such as metal or plastic. It is best for stiffening small paper parts that would otherwise be too delicate—railings, propeller blades, anchors, radar, and so on. Do not let CA get in contact with white glue unless the latter is completely dry. The white glue blob will curdle and expand into an unsightly mass that is difficult to remove.

Do not use rubber cement or mucilage, as both glues will fail over time. While some modelers use glue sticks for laminating paper onto cardstock, for large pieces I prefer a spray adhesive like 3M Super 77. It provides an even coat that doesn’t warp paper. However, you must be extremely careful when spraying and handling the sticky pieces, and only use a light, misting coat. Super 77 is difficult to remove, and the recommended solvents are nasty.

Examine each part carefully before cutting. Many paper models do not include gluing tabs, so you should incorporate them as you cut out the pieces. Gluing tabs will help strengthen bonds and keep parts in alignment. Joints where two pieces butt together edge-to-edge should be reinforced with a backing piece of scrap card, whenever possible. Be sure to use sharp knife blades, and remember to change them often. #11 X-acto blades are cheap, and it is less tedious cutting out small pieces when you have clean slices. You should also invest in a cutting mat. Most have a vinyl "self-healing" surface bonded to a hard backing. This not only saves your table or desk top from accidental mutilation, but it extends the life of your knife blades. Using scrap cardboard as a cutting board is not really so economical. As the cardboard becomes scored with cuts, there is the increased possibility that the blade will jump or swerve when cutting, or go through the cardboard into the surface below. Also, thick cardboard rapidly dulls the knife point.

It is possible to add decals to your paper model, if you wish. Dry-transfer decals should be applied and sealed with spray finish before assembly, since you need to burnish them against a flat surface for best results. Be careful when handling or bending any piece with dry-transfers, as they are delicate and may flake off. You can use water-based decals providing the model is well-varnished, and you immediately blot up all moisture before it soaks into the paper. Do not use any decal-setting solutions, as the alcohol will attack the inks.

Due to their lightness, paper ship models with tall masts or superstructures can be top-heavy. They are also vulnerable to open windows and room fans. To prevent your models from keeling over or skittering off the shelves, you should incorporate ballast during assembly. You don’t need too much—only a couple pennies or a few finishing nails glued as low as possible within the hull will be effective. Even flat-bottomed or waterline ship models will benefit from a little weight.

Dry-fitting parts before applying glue can avoid messy corrections later, but don’t worry if your first efforts are less than perfect. One of the nice things about digital paper models is that when disaster strikes you can crumple your mistakes into a ball, fling it across the room in utter frustration—and then calmly return to your computer and hit the "Print" button for another try. It can be very therapeutic. I know.

Dusting paper models can be difficult, due to their delicate nature. (Unlike wood or plastic models, you can’t simply rinse a paper model under a faucet.) A pressurized air can is probably the best option. You might want to display your model in a dust-proof case.

If you need to store your models, you might want to consider florist bouquet boxes or Christmas wrapping paper boxes for long ships. There are also a wide variety of mailing packages available. Toss in a few packets of silica gel you find in medicine bottles or candy tins (those small paper packs labeled "DESSECTANT—DO NOT EAT"). Keep in mind that most cardboard boxes are not ph-neutral, so direct contact with the cardboard should be avoided to prevent yellowing. Storing your paper models for prolonged periods in cardboard boxes may expose them to acid fumes. (Yes, "white metal disease" can strike paper models, too.) Shoeboxes may also contain traces of leather tanning acids. An occasional "airing out" of your model should delay any "acid air" disintegration or yellowing.