Yes, I was vaguely aware of the bullfighting origin - but it's a common enough expression in its figurative usage.

As you state, term is related to a bullfigth. There is three steps (momentos) during bullfigth.

a) Primer tercio where a Capote confronts the bull.

b) Segundo tercio where horses and banderillas: se pica el toro. (in order to stimulate his bravura).
c) Faena and if applicable killing. (faena y matar)

There is three circles on the plaza, the closes you go to the center danger rices.
Regarding art it might be talking about to change of position regarding a point, the way you will have a different perspective.

i think the emphasis should be in 'radical' / 'sudden'

or "turn over the page"

:)

See ref.
http://www.britannica.com/EBchecked/topic-art/84444/76317/A-...
Note: this shows part of the final act (the killing), but before there are others: picador, banderillas, etc.

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Note added at 36 mins (2010-05-04 18:23:25 GMT)
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See a better reference :The three acts of a bullfight
http://www.faace.co.uk/bfacts.htm

a step forward in the approach of the object and the concept ...

This is my interpretation of the three "tercios" of a bullfight.

La corrida se basa en tres tercios(De varas,De banderillas y de muerte) y el torero ha decidido cambiarlos o variarlos excepto el último que es el de muerte.

Another option with this meaning:

Sports of The Times - For Giants' Tom Coughlin, Live and Learn ...
27 Jul 2008 ... But Coughlin said the main impetus for **his sea change came** from his wife. “My wife has always been critical,” he said, meaning in a positive ...
www.nytimes.com/2008/07/27/sports/football/27vecsey.html - Similar

Battle of Wills by Joseph Bottum - The New Criterion
And he was a liberal, after **his sea-change** in the late 1960s, a darling of the New York Review of Books. But, conservative or liberal, the hunger to matter ...
www.newcriterion.com/articles.cfm/Battle-of-Wills-3957 - Cached

Entrepreneur trumps up Whitsundays Media Man Australia
... and a Newport "boy" originally, Greg relocated to Airlie this past October as part of **his sea change**, and it's been pretty smooth sailing since. ...
www.marvelheroescasino.com/articles/entrepreneur_trumps.htm... -

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Note added at 1 hora (2010-05-04 18:50:27 GMT)
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Gallery owner and artist Murray Charteris has spent the last decade as head of graphics at Channel Nine Brisbane and has recently **made his sea change** to Hervey Bay to fulfill his dream as a full-time artist. "I'm really excited to have this opportunity, this is a turning point in my life." Murray is quickly gaining a reputation in the art community for his dynamic, energy filled fine art. His bold colours and powerful compositions come together to produce artwork that is increasingly sought after.
http://www.murraycharteris.com/About_Gallery.htm



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Note added at 1 hora (2010-05-04 18:53:12 GMT)
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"His sea change towards....."

ReadWriteTalk » Blog Archive » Ben Elowitz - CEO, Wetpaint
29 Oct 2007 ... common with thousands of other fans with the same artist or team, ..... we see a **sea change towards** wanting to have a wiki-like consumer ...
readwritetalk.com/2007/10/29/ben-elowitz-ceo-wetpaint/ - Cached

MCV525 February 20th
The artist designed the cover artwork, as well as drawing specific character ...... note the driving force behind this **sea change towards** 'casual' sequels. ...
issuu.com/intentmedia/docs/mcv_issue525 - Cached - Similar

Switching one sports metaphor for another, that curiously showed up when I Googled the combination: Now they change tack and return to flamenco with their new show, "Cambio de tercio". With the modern vision that has always characterized their productions, ...
www.esflamenco.com/scripts/news/ennews.asp?...1247 On tack: If you change tack, you use a different method for dealing with something. http://www.usingenglish.com/reference/idioms/change tack.htm... Sailing Club: Definitions - [ Traducir esta página ]
Tack: A corner of a sail. The lower corner of the luff, the leading edge. Tack: To turn the boat into the wind so that you change from one tack to another ...
quis.qub.ac.uk/sailing/techinfo/definit.htm -