
InPhilippine architecture, thecapiz shell window is a type of window with smallpanes that use the translucent and durablecapiz shell (windowpane oyster shell) instead of glass. The Chinese were presumably the first to use the shell, the dissemination of which use has been credited to the Portuguese; extensive and widespread use of the shell for windows and other handicraft products as a substitute for the then more scarce and more expensive glass was seen in Portuguese settlements as well as in India in the 17th century.[1]
During the length of theSpanish colonization of the Philippines, churches and homes used thecapiz shell for windowpanes, cabinet decorations, and handicrafts starting in 1755, while before this period the seashell was only used widely in the decoration of weapons, clothes, and trading goods. It is believed that the shell was first used architecturally in the making of slide windows for the churches of the Catholic Church in the Philippines. Philippine text history confirms the continued popularity of thecapiz shell as a Philippine architectural element in the 19th century through the entry "Capiz" in the 1860 edition ofVocabolario de la lengua tagala, the first dictionary of theTagalog language; the entry for "Capiz" refers to it as "la Ventana" (the Window). Today, the shell is also used in the manufacture of decorative items, including mobiles, chandeliers, Christmas lanterns (theparol), and various other products.[2][1][3]

Panels from the early centuries of capiz-shell window-making show tightmortise and tenonlap joints on the frames, done using only chisels and hardwooddowels. The lattice work often show the delicatecapiz shell inserted into a less than 1/16" groove.[4]The flat shells ofCapiz, the Philippine province where the oyster is most abundant and after which the Philippine windowpane oyster has been called, can grow to over 150 mm in diameter, reaching maturity between 70 and 100 mm, making the size of the panes of Philippine capiz-shell windows variable.[2][5]
On June 12, 2020, theNational Museum of the Philippines launched an online exhibition titled "Placuna placenta: Capis Shells and Windows to Indigenous Artistry" alongside other government institutions' celebrations commemorating the 122nd anniversary ofPhilippine independence.[6]

In 19th-century Philippine colonial architecture,bahay na bato houses extensively used the capiz-shell window element. Designed to take advantage of tropical cool breezes, these houses' large windows were built at least a meter high and as wide as five meters. The typically sliding panels withconchas or lattice work (muntins) that would carry the windows'capis panes would be drawn shut when there is too much wind, with the house still taking in daylight during the storm.[7]
In the year 2000, there were at least 27 naturalkapis beds in the Philippines, the major sources being in Sapian Bay andRoxas City, Capiz;Oton andTigbauan,Iloilo;San Miguel Bay inCamarines Norte andCamarines Sur;Hinigaran andPontevedra,Negros Occidental;Mangarin Bay inMindoro Occidental; andPanguil Bay inMisamis Occidental.[8]