The best process to cosmetically restore most devices is to completely
disassemble them, clean the plastics in the sink, thoroughly dry them,
and then reassemble.
The most powerful tool you have in cleaning plastics is water, but other cleaning products may also help the process. Note that almost all other cleaning products are at least slightly abrasive, so be careful. You should scrub your plastics as little as possible to get them clean. Aggressively removing a stain may change the texture of the plastic, making it noticeably different from the plastic around it. This is always a trade-off; a slightly mistextured area of plastic is usually preferable to a dramatic scuff. You should strike the balance that feels right to you.
Cleaning products you might consider:
(Dish) soap is something you almost certainly already have and is effective.
Baking soda gives a deeper clean than dish soap since it’s powdered and inherently more abrasive.
Rubbing alcohol is very effective and works well without water. Useful if you’re unable to detach plastics from other water-sensitive parts.
Goo-Gone (mineral spirits) is the go-to solution for old adhesive (stickers or tape). It’s very effective, but not magic: get as much of the adhesive off as possible before letting the Goo-Gone sit for 30 minutes or more, and cleaning with soap, water, and dish brush to remove all remaining goo.
Magic eraser is a good substitute for baking soda and a lot of scrubbing. In my experience it doesn’t clean or affect surface texture any more or less than baking soda + scrubbing, but may be easier and/or more expensive.
Dissemble the piece you’re trying to clean into as many individual pieces as possible. Smaller, individual pieces are easier to clean and increase the likelihood you’ll get dirt out of every crevice.
On the other hand, some plastics lose their elasticity over time and can become brittle — Apple products from the mid-90s are especially notorious for being extremely difficult to work on without breaking. Whether or not to disassemble a piece in the first place is a trade-off: a slightly dirty piece is usually preferable to one whose plastics are cracked. As always, strike the balance that feels right to you.
Pay attention to anything attached to the plastics:
Paper labels are likely to get damaged when cleaning with water
Plastic or metallic labels are usually fine. Very long soaks (when bleaching plastic, for example) can sometimes discolor these, but washing in the sink is usually not a problem.
Painted metal Apple logos are usually fine, although the paint may start to come off if you scrub them or submerge them in chemicals (like plastic bleach). These are relatively easy to remove via a hole on the plastic behind them.
Metal shielding or even electronic components may be permanently attached to plastics with melted standoffs. Metal shielding is unlikely to get damaged with water but will need to be dried thoroughly. Electronic components will get damaged. They can sometimes be removed by melting the standoffs with a heat gun, but this is tricky work.
Some plastics are coated on the inside with a metallic surface that acts as electronic shielding. This coating is fine to expose to soap and water, although I’ve seen weaker coatings be stripped off by plastic bleach.
Cleaning plastics without disassembling
Rubbing alcohol cleans well and evaporates quickly, so you don’t have to worry much about it getting into unwanted places or needing a lot of time to dry.
Soak a paper towel or rag in rubbing alcohol and rub the plastic down
Soak a cotton swab to clean grooves or crevices. Cotton swabs are also useful for light scrubbing. Regular cotton swabs work well most of the time, but for specialized areas I also use precision tip cotton swabs, which are tapered to a sharper point
Dip an old toothbrush in rubbing alcohol for gentle scrubbing when a rag isn’t enough
Cleaning disassembled plastics
If you’re able to disassemble the piece you’re trying to clean, you can wash it in the sink like you’d wash anything else. Dish soap is a useful cleaning agent, but I use an empty bottle of baby powder that I’ve filled with baking soda. You can puff the baking soda over the plastic, and then rub it in with the palms of your hands or use an old toothbrush for small crevices or more stubborn scuffs. Rinse thoroughly and leave to dry on the counter or outside in the sun.
Cables are often difficult to detach from their pieces — soak a paper towel in rubbing alcohol, wrap it around the cable, and squeeze firmly as you pull the cable through.
Old plastics often become discolored due to the chemical structure
breaking down. Bromine, which is used to make plastics fire retardant,
can break down when exposed to ultraviolet light and cause old
plastics to turn yellow. The plastic’s original color can be
restored by bleaching the plastic with hydrogen peroxide as an active
ingredient (often called retrobrighting).
While it is very easy to change the color of plastics using hydrogen peroxide, controlling the process such that you get an even coat of the desired shade takes effort and practice. Those techniques will be covered in another article.
Removing scratches from glossy plastic
Even small scratches are noticeable in glossy plastics, and especially translucent plastics (since scratches can affect the way light moves through the plastic). You can improve the appearance of glossy plastics by polishing these scratches out.
Counterintuitively, polishing plastic works a lot like sanding imperfections out of wood: to remove scratches, you start with a heavy abrasive and follow with softer and softer abrasives until it’s smooth again. Because of this, it’s important to only use polish on glossy plastics. Trying to polish scratches out of textured or matte plastics will produce uneven results, since you’ll be abrading the texture away.
There are many plastic polishes available, but I use Novus No. 3, Novus No. 2, and a buffing wheel.
For scratches that are noticeable as individual scratches (rather than just micro scratches on the surface), start with Novus No. 3. Squeeze a small amount of polish onto the plastic, and rub firmly perpendicular to the direction of the scratch with a rag. Remember, you are abrading the scratch away, so vigorous rubbing is useful.
You can repeat this process until the scratch is removed or reduced to your liking. Note that the plastic around the scratch will likely look less polished after this step since you’ve just been rubbing it with a (relatively) strong abrasive.
Next, or if you don’t have large individual scratches, move on to Novus No. 2. Squeeze enough polish onto the plastic such that you can rub a very thin layer over the entire surface area. Too much will just take a long time to dry. Rub in with a rag in a circular motion — it doesn’t need to be as firm as the first step. Wait until the polish dries to a haze, then wipe off with a clean rag.
After this step your plastic should feel notably smooth, and look almost as glossy as you want it.
The final polishing step is buffing. Although you can do this with a soft cloth, I find it much more efficient to attach a buffing wheel to a power drill. There are many options available — I use a 6” Fine buffing wheel from SCOTTCHEN on Amazon, attached to an arbor I bought at my local hardware store. I set my drill to full speed, and then move the spinning wheel back and forth over my plastic for 30-60 seconds. Buffing for longer, or with a softer wheel, will result in a smoother surface.
Take care to make sure you’ve removed all the polish from your plastic — it’s common to find whorls of Novus No. 2 even after you’ve wiped and buffed your surface. Polish can also get into crevices and will dry to a light brown color. You can do a final clean with soap and water (using a dish brush to clean out crevices) if you like, followed by drying thoroughly.