The Commonwealth of Australia started printing its own stamps in 1913. Before that, each of the several States had printed their own.
The first major stamp series to be printed after 1913 by the Commonwealth was the Kangaroo and Map, often abbreviated to roo. (There are later stamps with just a kangaroo and no enclosing map, but these are of little value comparatively, so it can be better to use the full term Kangaroo and Map).
The roos reached high face values, the highest being two pounds. That would have been similar to the average weekly wage in 1913. Even in 1959, my first job paid a mere 6 pounds per week.
The stamps with values up to 5 shillings were printed in mono colour on white paper. The five shilling, some one pound and all two pound roos were printed in bi-colour also on white paper, using a master engraving from which the central roo had been erased, then making a second pass through the presses to imprint the roo. The exception was that some one pound stamps were in monocolour grey. This in turn made more valuable the other one pound stamp, in various shades of brown roo and blue background, for there were fewer of them.
The hi-valued roos were printed on various papers. In the simplest case, the five shilling grey and yellow (or related shades) was printed on paper with First Watermark, Second Watermark, Third Watermark, Small Multiple Watermark and Commonwealth of Australia ( C of A) Watermark. Thus, a complete collection of roos should have these 5 watermarks at least. Further variations happen from there - there can be large or small punctures of "OS" for "ON SERVICE" or similar words and there can be shades of colour and there can be varieties like inverted watermarks and misprints and "Cancelled to Order (CTO)". These are the stuff of book catalogues and expert texts.
Different combinations of watermarks were used for the remaining high-valued roos, the 10 shilling, one pound (two types) and two pound. The First Watermark two pound roo in grey and rose is the routine stamp with the highest catalogue price in all of the Brusden White catalogues.
(In money terms, there were 12 pence to the shilling and 20 shillings to the pound. These Imperial units were replaced by Decimal on 14 February 1966, long after the last roos were printed).
I wish to stress that the world of philately is awash with Australian collections bereft of the high valued roos. Many collectors baulk at the expense of the bi-colour roos and collect a token number of used stamps or none at all.
The point of this article is to suggest to collectors new to Australian stamps that they START WITH THE HIGH VALUED ROOS. Yes, it hurts the pocket, but the effort is rewarded if or when the collection is to be sold or disposed of. The expert making the valuation of the whole collection will commonly turn first to the pages where the high-valued roos should reside, unmounted if possible.
A collection with a good selection of good quality bicolour roos will warm the heart of the valuer and the overall estimate of value will rise in turn. The valuer could well think "Here is a person who was well-advised, so the rest of the collection should reflect this".
Valuers will often calculate in detail the top 5-10% of stamps then make a bulk estimate of the remainders. If there is no top end, you will get a low valuation indeed.
If you accept the logic of starting your collection with the bi-colour roos, you will need to pay attention to quality. That is the subject of another of my essays that you can access from here.
This note has been about commercial considerations. There is another plane of appreciation of stamps and that is the plane of craftsmanship. The high-value roos are wonderful examples of steel engraving and electros from other metals, of inserted value plugs, of fine watermarked papers, of the skills of the printer and stamp maker. It is more rewarding to occasionally appreciate a small collection of good stamps than to flick through a large collection of modern material or material from other countries of lesser philatelic talent, hardly even glancing at the craftsmanship.
In these throw-away days of mass production and photo litho etc, you should gain real pleasure from just looking at fine specimens of the high-valued roos. If you doubt this, try designing and making one of your own. That will cause you to give the makers their proper respect for craftsmanship.
(I have made a CD that has all of the routine Australian stamps. You can appreciate the high roos from the careful scans on the CD as well, but nothing on the CD matches the smell and the feel of the real thing.)