Quality is, stricto sensu, a property of items which is represented in-game by the color of the item's name and (in most cases) by a title prefixed to the item's name. A dropped item can only have one quality, and an unboxed item can have 1 or 2 qualities. Extra qualities can be added through the use of strangifiers or unusualifiers — not counting rare exceptions from glitches (e.g. "Strange Normal" items) or forced creations by Valve employees.
Quality is overall a purely cosmetic property. When it changes even visuals beyond colored title text, it deals aesthetic changes like particle effects from Community (which once had a since-removed hidden 10% Damage boost) and Self-Made items, Decorated weapons' patterns, and some additional on-screen messages — these messages usually relay succeeded operations with an item. Valve quality weapons, when they are extremely rarely seen (especially in recent years), need not even have stat boosts.
Possible weapon qualities
Please see the table listed here.
Possible cosmetic item qualities
April 29, 2008 Patch
(Gold Rush Update
- [Undocumented] Added Unique quality.
March 18, 2010 Patch (First Community Contribution Update)
- [Undocumented] Added Self-Made quality.
September 30, 2010 Patch (Mann-Conomy Update)
- [Undocumented] Added Vintage quality.
- [Undocumented] Added Unusual quality.
February 3, 2011 Patch
- [Undocumented] Added Genuine quality.
June 23, 2011 Patch (Über Update)
- [Undocumented] Added Strange quality.
August 18, 2011 Patch
- [Undocumented] Added string for potential new item quality called "Completed".
September 2, 2011 Patch
- Updated the Strange quality color from gold (#CD9B1D) to orange (#CF6A32).
- [Undocumented] Updated the Rarity3 quality color from orange (#CF6A32) to brown (#70550F).
October 27, 2011 Patch (Very Scary Halloween Special)
- [Undocumented] Added Haunted quality.
June 11, 2012 Patch
- [Undocumented] Added "tobor_a" quality.
October 26, 2012 Patch (Spectral Halloween Special)
- [Undocumented] Updated Haunted quality color from #8650AC to #38F3AB.
March 19, 2013 Patch
- [Undocumented] Removed "tobor_a" quality.
November 12, 2013 Patch
- Added "Collector's" item quality with color #830000. "Collector's" items are created by completing special Chemistry Sets.
November 26, 2013 Patch
- [Undocumented] Updated Collector's quality color from #830000 to #AA0000.
September 17, 2014 Patch
May 28, 2015 [Item schema update]
- Added "restriction" and "map" quality.
July 2, 2015 Patch (Gun Mettle Update)
- [Undocumented] Added Decorated quality.
- Two unused item qualities referred to as Rarity2 (mentioned as Customized) and Rarity3 (mentioned as Well-Designed and Artisan) are specified in the game's files. Their colors are two shades of brown; #8D834B and #70550F respectively.
- The "Completed" quality is specified in the game's files, and its color is the same as the Unusual quality: #8650AC.
- The TF2 source code leak contains a mention to a possible variant or sub-type of Self-Made quality, called "SelfMadeCustomized".
- ↑ game/shared/econ/econ_item_constraints.cpp, line 91