Help your scaly items last

Inspired by questions I've been asked quite a few times about how well gloves last, here is an exhaustive list of my experience with scale knitting, with information that can help you care for your finished items, as well as a few tips on choices if you are making your own to make something that will last.
Generally you shouldn't have any problems with scaly items wearing out, but if you are worried about things that could make your items start to look scruffy too quickly you might find some information here helps you keep everything in top condition for as long as possible.

Scale Material Considerations
Aluminium Scales

These are in the most common in items I've sold and are available in the most colours.
Aluminium scales can have rough edges, which can wear the yarn over time. Normally the scales won't rub the yarn very much at all, as individually the scales are very light and as long as the yarn is thick enough they barely move around. This will become more important if you are regularly rubbing the scales the wrong way, for example wearing gloves when putting them on or taking them off under sleeves, or putting your hand in and out of a bag. Although doing these things shouldn't cause any immediate damage to the fabric, it's best to avoid any major pulling on the scales whenever possible to maximise life.
Aluminium scales are not particularly reactive in water, and all the non silver (and most of the silver ones in item's I've made since late 2013) are anodised which helps protect them further. All non-anodised scales will have a naturally grown thin layer of aluminium oxide (unavoidable in contact with air) which also helps protect them, however they may still suffer from water damage it's still best to avoid getting the scales wet and to dry them out again as soon as possible. Do not use direct heat to achieve this though, as the aluminium is very conductive and will get surprisingly hot and you may even find the yarn begins to melt!
Aluminium is not particularly hard, however the colour is anodised into the surface so small scratches general won't affect the finish.
Aluminium scales are not armour grade - if they are hit with a sword or other heavy blunt object for example in a re-enactment, they will dent permanently (also you will certainly be bruised if you hit them hard enough to dent them). This may cause some of the pointed ends to stick up which aside from altering the aesthetics is more likely to scratch and damage other items or people.
Plastic Scales
As I write this none of my sold items include plastic scales, but I have just gotten in the first batch and they look great. They're generally safer, lightweight and water resistant, making them a prime candidate for kids sizes, however they're only available (at least right now) in black and transparent.
In contrast to aluminium scales, these have smooth edges and are much more resistant to water. They may have two noticeable sprue marks were they have been cut from the main piece after moulding, but they shouldn't cause any damage to the yarn. If they get wet it's still a good idea to dry them out as soon as possible, as damp yarn can become home to unwanted microbes.
These scales are the same colour through, so if scratched will not stand out in a different colour, even if the scratch is deep.
Plastic scales are very not armour grade - if they are hit with a sword they will probably shatter, and may leave sharp edges which at high impact could cut into your arm.
Other Materials
Although I do not normally stock them, there are plenty of other materials that are available for scales, so if you are making your own items then you may want to use something else.
Most likely it will be a metal, and although some metals are softer and will punch more smoothly it's best to assume that it may have a rough edge that can wear on the yarn. Many metals are more reactive than aluminium and will react even in damp environments. Look up your metal and find out general information about how it will act if you get it wet. If unsure, make every effort to avoid getting it wet, dry it quickly, and to keep it away from damp atmospheres.
Some other materials are technically armour grade. However, if you knit them into fabric, your item will not be armour grade as they can shift too easily past each other. If a scale claims to be armour grade then you can be confident that it shouldn't dent if hit, however the flexibility of the knitted base means it will not afford you any protection and you will almost certainly bruise or worse.

Special Item Considerations
Yarn only items are safely covered by other areas, however there are a few things that need a little extra care.

Baby dragons, while partially scaly, have shape and pipe cleaners. Due to the pipe cleaners particularly they are a bit more difficult to take care of. They should avoid ever getting wet (or feeding after midnight*) and if they do, make sure the spread their wings and limbs wide and allow them to dry fully. Although the pipe cleaners make the wings moderately poseable, their primary function is to bear the weight of the wing scales. If harshly bent too many times to pose the wings, the pipe cleaners will eventually break, so try to stick to gentle curves and minor adjustments to angles at the elbow and shoulder.
The pangolin, like the baby dragon, is also stuffed, and is a lot chubbier. The pangolin is probably at the most danger from getting wet as the stuffing inside is quite bulky, and even if you dry the surface the inside may still hold some water for a long time after, which aside from standard damp concerns can cause discolouration and reactions in the scales. It's best to make sure the pangolin does not get wet, or if it does to allow it to dry thoroughly for several days minimum in a very dry place.
*Actually avoid feeding your scaly critters at all, they don't know how to eat regular food and they'll just make a mess. Your scaly animal will hunt down suitable food for itself when you're not looking.

Manufacturing Considerations
When you're planning to knit an item, you want it to last as well as possible. There are a few things you can do to help your item work at its best.
Use the strongest, thickest yarn suitable for your project. The patterns available here all recommend aran or worsted weight, because this is the best compromise between strength, holding power, and ease of knitting. If you want to make a particularly heavy duty item and have the time to work with more awkward yarn, something chunky will improve the life of your item. A thicker yarn holds the scales down more firmly, so they won't move around which in turn reduces wear (particularly with metal scales' punched holes). The thicker yarn can also take more wear intrinsically.
I personally favour James C Brett's Marble Chunky, as it's structure is particularly suited for long wearing. The yarn has two thick ply twisted around each other, each with a strong core thread; the coloured yarn visible is not structurally integral, and provides a thick barrier of protection to the inner core. Any normal chunky yarn is generally good, if you are comfortable working with such a thick yarn on small needles (you may need to switch the needles down a size to make sure you keep gauge) and pulling it through the small holes in the scales.
If your item is likely to receive heavy wear you may want to choose plastic scales, or use a small round file to manually smooth each individual scale. If you do this, be careful not to damage the colouring too much! If your item might get wet, you're best to use the plastic scales, which are much more suitable for wet conditions.
If you think you might get ambushed by a medieval knight while wearing your item, consider using armour grade scales. They may not give you much protection (although it's probably better than nothing) but it will ensure that once you've defeated your foe your item should not have been substantially damaged.
If a scale does not explicitly state that it is armour grade, assume it is not.