# Junk

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 perks

As material for a gizmo shell, Junk does not grant any possible perks.

## Devices

This list was created dynamically, and shows the first 100 items alphabetically.

## Research

The percentage of junk can be reduced through research. The junk rate is a simple multiplier of the base junk chance: for example, maple logs have a base junk chance of 50.5%, so a player who has researched Junk chance reduction 9 will get a junk rate of $50.5\%\times 0.8=40.4\%$ . level Research name Junk rate Reduction
1 None 100% 0%
34 Junk chance reduction 1 99% 1%
49 Junk chance reduction 2 97% 3%
64 Junk chance reduction 3 95% 5%
69 Junk chance reduction 4 93% 7%
78 Junk chance reduction 5 91% 9%
83 Junk chance reduction 6 88% 12%
91 Junk chance reduction 7 86% 14%
95 Junk chance reduction 8 83% 17%
105 Junk chance reduction 9 80% 20%

## Obtaining junk

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 bulk-obtaining junk, but provides useful additional materials.

## Calculation

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:

$J={\begin{cases}100-1.1\times L&L<75\\f(L)&75\leq L<90\\0&L\geq 90\\\end{cases}}$ 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 best-fitting 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

${\hat {J}}={\big \lfloor }J\times g(r)\times 1000{\big \rfloor }\div 1000$ 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.

## Update history

The update history project is a work-in-progress – not all updates to this topic may be covered below. See here for how to help out!
• patch 22 February 2016 (Update):
• Junk chances ending in .0 will no longer be incorrectly displayed as too low.
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