Release date  25 January 2016 (Update) 

Rarity  Other 
Level  1 
Experience  0 
Description  
There may be some use to this stuff, somehow? 
Junk is a material used in the Invention skill. Items that can be disassembled have a junk chance, which determines the likelihood of receiving junk as a component. Using the Analyse ability on an item displays a percentage chance of receiving junk from disassembly.
When disassembling an item, the first roll determines whether or not junk will be received. A second roll will determine what material is given if not junk.
Possible perksEdit
As material for a gizmo shell, Junk does not grant any possible perks.
DevicesEdit
Item  Skill  Materials 

Junk refiner  22 Invention 

ReductionEdit
The percentage of junk can be reduced through research.
Research  Level 

Junk chance reduction 1  34 
Junk chance reduction 2  49 
Junk chance reduction 3  64 
Junk chance reduction 4  69 
Junk chance reduction 5  78 
Junk chance reduction 6  83 
Junk chance reduction 7  91 
Junk chance reduction 8  95 
Junk chance reduction 9  105 
Obtaining junkEdit
Most of the time when disassembling items for materials, junk is an unwanted item  getting junk means the player is not getting the simple parts or powerful components or whatever other material is the goal. However, junk may be wanted in bulk to make junk refiners, which provide the refined components needed to make B.A.N.K. Standers or an alchemical onyx.
Getting significant amounts of junk is mainly about disassembling items which have a high junk chance and many materials, like bronze 2h swords, shortbows, etc. A calculator of such items is here.
Alternatively, maple logs (or other items that aren't optimal for junk) items can be disassembled to get simple parts with junk as a side effect. This is far less efficient for bulkobtaining junk, but provides useful additional materials.
CalculationEdit
The (base) junk chance of the vast majority of items depends primarily on the item's 'level'. For many items, this is the level to use or obtain the item in some way, for example:
 Most equipment use the level needed to equip
 Seeds use the Farming level to plant
 Logs use the Woodcutting level to cut
 Runes use the Runecrafting level to make
 Items that do not have an associated level usually use 1
This level may be distinct from other levels associated with the item, like required levels to earn the item, equipment tier, etc. This level is also used in calculating the item's disassembly experience. An item's level is 1 at a minimum.
Augmented items of equipment level 4 and higher have a junk chance of 0.
There are two distinct cutoff points where the formula for junk chance changes significantly: 75 and 90. In addition, arrows and bolts follow a slightly altered formula.
In the following formulae:
 $ J $ is the base junk chance as a percentage
 $ \hat{J} $ is the junk chance including reduction
 $ L $ is the item level
 $ f(L) $ is a function that maps level to junk chance in the 75–89 range
 $ r $ is the junk chance reduction researched (0 to 9)
 $ g(r) $ is a function that maps the reduction research number to a multiplier
 All results are truncated to 1 decimal place
 General
As mentioned, there are two cutoff points  creating 3 formulae  for junk chance for most items. This is summarised as follows:
$ J = \begin{cases} 100  1.1 \times L & L < 75 \\ f(L) & 75 \le L < 90 \\ 0 & L \ge 90 \\ \end{cases} $
Where $ f(L) $ is given by the following table:
$ L $  $ f(L) $  $ L $  $ f(L) $  $ L $  $ f(L) $  

75  4.2  80  2.3  85  1.0  
76  3.8  81  2.0  86  0.8  
77  3.4  82  1.7  87  0.6  
78  3.0  83  1.4  88  0.4  
79  2.7  84  1.2  89  0.3 
The bestfitting curve for this data set is approximated as:
$ f(L) \approx 99.1  2.089 \times L + 1.1 \times \left( \frac{L}{10} \right)^2 $
 Ammunition
Ammunition uses the 'under level 75' formula from above, but the level value is halved (and rounded down, but not less than 1).
$ J_{ammo} = 100  1.1 \times \mbox{max} \left ( \left \lfloor \frac{L}{2} \right \rfloor, 1 \right ) $
 Reduction
Junk chance reduction is a simple multiplier of the base junk chance, given by
$ \hat{J} = J \times g(r) $
where $ g(r) $ is given by the following table:
$ r $  $ g(r) $  $ r $  $ g(r) $  

0  1  5  0.91  
1  0.99  6  0.88  
2  0.97  7  0.86  
3  0.95  8  0.83  
4  0.93  9  0.80 
This means that items with a higher junk chance get a much larger benefit from junk chance reduction than items with a lower junk chance.