Introduction. "Kiloware" is the name given to stamps sold by weight, normally still on the backing paper as they've been cut or torn from envelopes. I don't know how far back the term goes; certainly it was in use when I first became involved with dealers and auctions and magazines about the early 1970s. An alternative name used then (but not often heard now) was "mission mix". I've always had the impression that this was originally from religious groups in Ireland who collected stamps from the public and sold them - sometimes directly to collectors - to raise funds. Another term which has gone out of use is "bank mix" which would be (as you might guess) stamps collected in a bank, so that there were usually lots of higher values and neat postmarks. Almost always, the original source of kiloware is charities. Buying kiloware has always been a popular way for collectors to obtain stamps for their collections, for various reasons (see "Advantages" below). For many new collectors it would be their introduction to the hobby. In recent years the hobby has gradually changed, as have the ways in which stamps are traded, and the ways charities work. Over the years many charities - from small local to massive global - have raised funds through collecting kiloware and selling it on. Most charities would sell to dealers, some would sell direct to collectors. Famously, BBC's Blue Peter programme ran a scheme collecting stamps for their Christmas appeal. Illustration; A good quality world kiloware mix, well trimmed and with good variety.

The Advantages of Kiloware.
1. It's normally a low cost source of stamps for collectors. The stamps should cost nothing to the charity *, and a dealer has minimal work to do.
2. It's usually a good source of some of the more recent issues commercially used. Many collectors prefer used stamps to mint, and many of these prefer stamps that have actually been through the post to ones which have been "cancelled-to-order".
3. There's the chance of good finds. Bear in mind that scarce stamps scarcely turn up, and rare ones rarely ! It's not unusual for collectors to find stamps worth a few pounds just now and again - the possibility of coming up with a really stunning gem is probably in line with the chances of a major lottery win.
4. In many cases the purchase of kiloware will support a charity (either directly or through a trader).
5. It can be really quite enjoyable and therapeutic. Many people find great enjoyment just sitting with a mixed bag of stamps, sorting through to see what can be found. It can absorb your attention for hours !

The Disadvantages of Kiloware.
1. Collectors buying kiloware will normally see diminishing returns. So if a general world collector gets a general world bag and finds a hundred stamps needed for their collection, a second bag might give them ninety, and a third seventy, and so on. Eventually they get to the point where it's not worth doing.
2. Charities can only sell on what they are given. If they get donated good stuff, that's great for everybody, but sometimes they'll be given bad stuff.
3. "Bad stuff" is most often what you might call "second time around the block" stamps, where a collector has got themselves a bagful, taken out everything they wanted for themselves, anything they think their friends might like, or that they can sell, and then donate the remainder back to a charity. That's not a big problem if that one "bad stuff" bag gets amalgamated with dozens of other better donations, but can otherwise lead to dissatisfaction.
4. Another source of poorer mixes is where a charity is gleaning the best out of what comes in. This is most often where they have a philatelic volunteer who can recognise the stamps that can be sold separately. That raises extra funds for the charity, but the downside is that the mix they are left with is rather lacklustre. This is not a common problem.
[If you happen to get a really poor mix from a charity or a dealer, it is worth pointing this out. You shouldn't expect a refund, as kiloware is accepted to be a bit of a gamble, but it is useful for the seller to have the feedback.]

"Unsorted" vs. "Picked"
It is always best to be the first person to sort through a batch of kiloware. That way, someone else will not have had a chance to make the finds before you. However, as mentioned above, there can be ways in which the kiloware can be picked over before it gets to the charity, or to the dealer.
Most professional dealers do not pick over the kiloware they sell. Consider this; if a collector spends an enjoyable evening sorting through a big bag of stamps, and finds a few that they consider to be worth a few pounds each, they'll think of that as time well spent - but a dealer will not want to spend £10-worth of their time hoping to find stamps worth £5.
The best approach, if you are in the habit of buying kiloware, is probably to try different sources. But don't write one off just because of one bad bag.

A Note Regarding the Present State of Kiloware.
Things have changed in recent years. Going back a decade or two, most of the stamps charities were given would be from current or recent mail, but they would always have some that people had from clearing out an old house, or going through old family papers. They might therefore have gathered in a year, say, 19kg of generally new mix plus 1kg of older, so the mix looked like new stuff and was a good source of recent stamps.
The current situation is that people actually get very few stamps in the mail. Charities get smaller amounts handed in, so the same charity might now be getting only 2kg of new mix, but they are still getting the 1kg of older stamps, and the mixture appears less appealing to the collector looking for newer issues.
Almost everything we get now is like that, with a fair number of older stamps included, and I'm afraid collectors will just have to get used to it !

Self-Adhesives.
Many stamps found in modern kiloware are self-adhesive, and very few of them can be floated or soaked off with water. The best way of keeping these in a collection is simply to try to trim the backing paper in a regular way, and mount or store them as normal.

The "Elephant in the Room" !
The benign world of kiloware has always been tied up with the murky world of unfranked stamps. There is a long history of stamps not being postmarked, and of people taking them off the envelope and using them again. In the UK, and similarly in other countries, it is illegal to do so. The Post Office has historically turned a blind eye to individuals doing this with an odd stamp here and there, but sees high-volume re-use of stamps as a threat to their revenue. Numerous people have been taken to court and punished for the "industrial" re-use or re-selling of unfranked stamps. See our longer article at this link.

A Kiloware Tale of Rarities In 2001 the German Post Office was set to issue a stamp showing Audrey Hepburn. Before it was issued her son objected to the image used being one that had been altered to show her smoking, and would not give permission. That stamp design was not issued, but an unknown Deutsche Post employee "pocketed" thirty sample examples of the stamp and used them to send his own mail. So far only five of these have been found, one selling in auction for €67,000. In theory, another twenty-five might still be found . . . . and some of these might still be in kiloware. Image courtesy of Auktionshaus Ulrich Felzmann GmbH & Co., Germany

Footnote.
* I've come across a couple of exceptions to this. In one case a UK-wide charity offered to have kiloware picked up free from members of the public, so they were having to pay carriage to get stamps in. In another, a charity asked people to send in their stamp donations by post, but some people would underpay the postage and the charity had to pay the Post Office's surcharge (therefore sometimes paying a couple of pounds to get in stamps worth less than 50p).