In comparison to later fighters, the improved F-5E had some weaknesses; these included marginal acceleration, rearward visibility, and fuel fraction, and a lack of Beyond Visual Range (BVR) weapons once such radar guided missiles became reliable during the 1980s. The F-5G, later renamed the F-20 Tigershark, aimed to correct these weaknesses while maintaining a small size and low cost to produce a competitive fighter. Compared to the F-5E, it had 60% more power, a higher climb rate and acceleration, better cockpit visibility, more modern radar and BVR capability, and competitive performance with fourth generation fighters. Like the F-5, it had better cost effectiveness as it had the minimum necessary features relative to its competition to perform its air superiority mission. As an example, in the 1960s and early 1970s, the F-5's lack of BVR missiles was not a significant disadvantage as the kill rate of such missiles was approximately 8% to 10%, and the performance and loss of surprise (radar warning to the enemy) cost of carrying them was not practically justified. By the early 1980s, the American AIM-7 Sparrow radar-guided missile in its "M" version was realistically exceeding a 60% kill rate, and was integrated onto the F-20. Brigadier General Chuck Yeager, test pilot and the first man to break the sound barrier, referred to the F-20 as "the finest fighter". Despite its performance and cost effectiveness, the F-20 lost out for foreign sales against the similarly capable, more expensive F-16, which was being procured in large numbers by the U.S. Air Force and was viewed as having greater support.
A secco or fresco-secco painting is done on dry plaster (secco meaning "dry" in Italian). The pigments thus require a binding medium, such as egg (tempera), glue or oil to attach the pigment to the wall. It is important to distinguish between a secco work done on top of buon fresco, which according to most authorities was in fact standard from the Middle Ages onwards, and work done entirely a secco on a blank wall. Generally, buon fresco works are more durable than any a secco work added on top of them, because a secco work lasts better with a roughened plaster surface, whilst true fresco should have a smooth one. The additional a secco work would be done to make changes, and sometimes to add small details, but also because not all colours can be achieved in true fresco, because only some pigments work chemically in the very alkaline environment of fresh lime-based plaster. Blue was a particular problem, and skies and blue robes were often added a secco, because neither azurite blue nor lapis lazuli, the only two blue pigments then available, works well in wet fresco.
It has also become increasingly clear, thanks to modern analytical techniques, that even in the early Italian Renaissance painters quite frequently employed a secco techniques so as to allow the use of a broader range of pigments. In most early examples this work has now entirely vanished, but a whole painting done a secco on a surface roughened to give a key for the paint may survive very well, although damp is more threatening to it than to buon fresco.
A third type called a mezzo-fresco is painted on nearly dry intonacofirm enough not to take a thumb-print, says the sixteenth-century author Ignazio Pozzoso that the pigment only penetrates slightly into the plaster. By the end of the sixteenth century this had largely displaced buon fresco, and was used by painters such as Gianbattista Tiepolo or Michelangelo. This technique had, in reduced form, the advantages of a secco work.
The three key advantages of work done entirely a secco were that it was quicker, mistakes could be corrected, and the colours varied less from when applied to when fully dryin wet fresco there was a considerable change.
For wholly a secco work, the intonaco is laid with a rougher finish, allowed to dry completely and then usually given a key by rubbing with sand. The painter then proceeds much as he would on a canvas or wood panel.