An extract on #grafflife
The Northrop YF-17's aircraft's main design elements date from the F-5 based internal Northrop project N-300. The N-300 featured a longer fuselage, small leading-edge root extensions (LERX), and more powerful GE15-J1A1 turbojets. The wing was moved higher on the fuselage to increase ordnance flexibility. The N-300 further evolved into the P-530 Cobra. The P-530's wing planform and nose section was similar to the F-5, with a trapezoidal shape formed by a sweep of 20 at the quarter-chord line, and an unswept trailing edge, but was over double the area. While the YF-17 lost its bid for the USAF lightweight fighter, it would be developed into the larger McDonnell Douglas F/A-18 Hornet.
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.