Domingos Antonio de Sequeira Paintings & Artwork for Sale | Domingos Antonio de Sequeira Art Value Price Guide

Nov. 25, 2024
DOMINGOS SEQUEIRA (1768-1837) Retrato do filho do Conde de Linhares Impressão da gravura de 1824 Dim. aprox.: 24 x 19 cm.
Est: €80 - €160
DOMINGOS SEQUEIRA (1768-1837) Retrato do filho do Conde de Linhares Gravura sobre papel Dim. aprox.: 24 x 19 cm.; Dim. total. aprox.: 48,5 x 44 cm. Manchas, vincos e defeitos. Emoldurada.
Palácio do Correio Velho
Oct. 22, 2024
Domingos Sequeira Attrib. (1768-1837)The Penitent Mary Magdalene
Est: €25,000 - €35,000
The Penitent Mary Magdalene Oil on canvas Depicting Mary Magdalene prostrated in a grotto, draped in dark robes, with her long hair loose and holding a skull in her right hand. Beside her lie a book and a rosary, emphasising the symbolism of spiritual contemplation and penitence57x41,5 cmDomingos António de Sequeira (1768-1837), one of the greatest masters of Portuguese painting in the late 18th and early 19th centuries, stood out for his style influenced by both Neoclassicism and the emerging Romanticism. Throughout his multifaceted career, he dedicated himself to historical and religious painting, engraving, and drawing, always displaying mastery in the representation of the human figure and a remarkable sensitivity in theme composition, establishing himself as one of the most notable Portuguese artists of his time (Markl, 2013). The parallels between the work we now present for auction and other depictions of Mary Magdalene created by Sequeira between 1796 and 1800 are evident, reinforcing the belief that this could, indeed, be an undiscovered work by the artist. The dramatic composition, combined with the technical finesse in the use of light and shadow, is characteristic of Sequeira’s oeuvre (Crespo de San Payo, 2009), further cementing his status as one of the leading figures in Portuguese painting of his era. A distinctive feature of this painting is the unusually masculine appearance of Mary Magdalene's body, particularly noticeable in the arm and leg of the figure. Although atypical, this could be explained by the hypothesis that Sequeira used male models for his pose studies, as suggested by some evidence in his graphic work (Markl, 2013). There is also the possibility that the artist initially began this canvas as a depiction of a hermit saint, which later evolved into the penitent figure of Mary Magdalene. Literature: Markl, Alexandra Josefina Reis Gomes. A obra gráfica de Domingos António de Sequeira no contexto da produção europeia do seu tempo. Tese de Doutoramento em Belas-Artes, Especialidade de Desenho, Universidade de Lisboa, Faculdade de Belas-Artes, 2013. Crespo de San Payo, Manuel Pedro Alves. O Desenho em Viagem: Álbum, Caderno ou Diário Gráfico. O Álbum de Domingos António de Sequeira. Tese de Doutoramento em Belas-Artes, Especialidade de Desenho, Universidade de Lisboa, Faculdade de Belas-Artes, 2009.
Veritas Art Auctioneers
May. 23, 2024
DOMINGOS SEQUEIRA (1768-1837) - Figural Studies
Est: €750 - €1,000
Pencil on paper. Preparatory study for painting. Dim.:26x17cm. Certificate of Prof. Bernardo Pinto de Almeida.
Marques dos Santos
May. 23, 2024
DOMINGOS SEQUEIRA (1768-1837) - Studies - Recto/Verso
Est: €1,200 - €1,600
Pencil and Indian ink on paper, double-sided, sided and straight. Preparatory study for painting. Dim.: 20x31cm. Certificate of Prof. Bernardo Pinto de Almeida.
Marques dos Santos
Jun. 05, 2023
DOMINGOS SEQUEIRA - 1768-1837
Est: €500 - €750
DOMINGOS SEQUEIRA - 1768-1837, Portrait of the son of the Marquis of Marialva, graphite on paper, moisture stains, unsigned Notes:1. Back with handwritten inscription, signed by Luís Xavier da Costa, with the following content: ""Desenho original do pintor Domingos Antonio de Sequeira para a litografia feita em Paris, em 1824: Retrato do filho do marquês de Marialva / (Existia na colecção Rebêllo Valente, do Porto, e foi-me oferecido em fevereiro de 1925 pelo Dr. A. Vasco Rebêllo Valente) / Veja os meus livros "A morte de Camões" e "A obra litográfica de Domingos Antonio de Sequeira" (Págs. 38 - 45 - 50-), onde vem reproduzido."; 2. "A obra litográfica de Domingos António de Sequeira" to which the inscription refers corresponds to the Offprint of «Arqueologia e História» - IV». Composition and printing of Tipografia do Comércio. Lisbon, 1925; 3. The story of this drawing, which led to a lithograph, is told by Luís Xavier da Costa in his aforementioned study 'A obra litográfica de Domingos António de Sequeira'; 4. In short, the story is as follows: the last Marquis of Marialva had a natural son with a certain Madame d'Ayala, when he was already in Paris, in the last years of his life. As the Marquis died on November 24th, suddenly and unexpectedly, the said Lady and the child - who would have been little more than a year old - were in a weak financial situation. Sequeira, who was also in Paris at the time, made the lithograph in order to carry out a kind of subscription among his friends to raise money to support the boy. In a letter to his brother-in-law, dated April 28, 1824, he writes 'o Retrato do filho do Marquês (destas vão 4) e que vai reprezentado o inocente izolado no mundo no meio da França esperando socorro' (daí estar representado com as mãos levantadas, como se estivesse a suplicar e sobre um mapa...). In the meantime, there are a number of official contacts at the Portuguese Court to appoint a legal guardian for the child. It is all this documentation that Xavier da Costa publishes. In one of the last letters, dated March 1825, it is said that the child ended up dying on the 1st of that month, due to 'a huma catharral complicada com a dentição'. The whole process was then without effect and had no continuity. Cabral Moncada Leilões acknowledges and thanks Doctor Alexandra Markl for confirming the authorship of the present, Dim. - 16 x 15 cm
Cabral Moncada Leilões
Jun. 05, 2023
DOMINGOS SEQUEIRA - 1768-1837
Est: €1,000 - €1,500
DOMINGOS SEQUEIRA - 1768-1837, Belvedere torso, graphite on paper, moisture stains and foxing on the paper, creases, signed. Notes: Cabral Moncada Leilões acknowledges and thanks Dr. Alexandra Markl for the confirmation of the authorship of this work, Dim. - 39,5 x 26 cm
Cabral Moncada Leilões
Mar. 27, 2023
DOMINGOS SEQUEIRA - 1768-1837 A female figure -
Est: €30,000 - €45,000
DOMINGOS SEQUEIRA - 1768-1837, A female figure -, oil on canvas, relined, restoration, unsigned, Dim. - 47 x 66 cm
Cabral Moncada Leilões
Mar. 27, 2023
DOMINGOS SEQUEIRA - 1768-1837 "Retrato de el-rei Dom João VI"
Est: €600 - €900
DOMINGOS SEQUEIRA - 1768-1837, "Retrato de el-rei Dom João VI", pencil on paper, defect on the paper with tear, unsigned, identified on 12-4-1929 by Luiz Xavier da Costa, collector stamp number 0457, Dim. - 19,8 x 17,3 cm
Cabral Moncada Leilões
Mar. 14, 2023
DOMINGOS ANTÓNIO DE SEQUEIRA (attr. a)
Est: €50 - €70
(Lisbona, 1768 - Roma, 1837) Studio di figura Inscritto: Dessein à l'estompe du chev.r Segueira, Portugais, présent du chev.re Antoine Montalvi, directeur de la Gallerie de Florence (1834). Matita e acquerello su carta applicata su carta, cm 18,2X24,3 PITTORE DEL XIX SECOLO La capra Amaltea Matita su carta, cm 16X22 (2)
Wannenes Art Auctions
Mar. 14, 2023
DOMINGOS ANTÓNIO DE SEQUEIRA (attr. a)
Est: €100 - €500
(Lisbona, 1768 - Roma, 1837) Studi di teste Firmata Cav. De Segueira e datata 1830 in basso al centro Penna su carta applicata su carta, cm 20,9X17,2 Inscritto: Croquis à la plume du Chevalier Segueira Portugais, fait à Rome en 1830. Cadeau du Cher Cavalleri Formatosi presso la Casa Pia di Lisbona, frequentò il corso di disegno e figura presso l'Aula Regia, lavorò come decoratore ma grazie alla benevolenza della regina Maria I nel 1788 partì per l'Italia e studiò all'Accademia Portoghese a Roma con Antonio Cavallucci. Successivamente, l'artista fu ammesso come professore all'Accademia di San Luca, dove dipinse la Decollazione di San Giovanni Battista, l'Allegoria della Fondazione di Casa Pia de Belém e Il Miracolo di Ourique, vincendo diversi premi concessi dalle accademie italiane. Tornato in patria nel 1795, fu nominato pittore di corte nel 1802 e condirettore di pittura per il Palazzo di Ajuda. Nel 1826 tornò a Roma dove si dedicò alla pittura religiosa, esprimendo una sensibilità già romantica.
Wannenes Art Auctions
Dec. 12, 2022
PRINT.- SEQUEIRA, Domingos António de.- [Sopa de A
Est: €600 - €900
PRINT.- SEQUEIRA, Domingos António de.- [Sopa de Arroios (Lisboa)].- Lisboa: s.n., 1813.- 1 copperplate;, One of the most famous engravings of Lisbon, open engraving and etching by Gregório Francisco Queirós (1768-1845) after an original by Domingos António de Sequeira (1768-1837), published in Lisbon, on December 17, 1813. Presents the following subscription: Dom. Ant. de Sequeira Ac. Rom. inv. del. et abrio os cont. das fig. — Greg. Franco. de Queiroz esculpio as figuras a Agoa forte e a buril em 1813. Clean, framed proof., Dim. - (gravura) 55 X 83 cm; (moldura) 68,5 x 96,4 cm
Cabral Moncada Leilões
Dec. 07, 2022
Atribuível a D.SEQUEIRA, D.João VI, óleo s/madeira
Est: €4,000 - €8,000
Atribuível a DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Retrato de S.M. El Rei Dom João VI Óleo sobre madeira Não assinado Dim. aprox.: 20 x 13 cm. Emoldurado. Moldura em madeira ornada por rica montagem em prata do séc. XVIII, em estilo rocaille, decorada com concheados, enrolamentos vegetalistas e entablamentos arquitectónicos, cinzelados e repuxados. Verso com argola para suspender. Sem marcas, ao abrigo do Decreto-Lei 120/2017, de 15 de Setembro - art. 2º, nº 2, alínea c). Dim. aprox. moldura: 43 x 31 cm. S.M. El Rei Dom João VI é retratado com casaca azul e dragonas douradas ao ombro. Ao peito é possível identificar o Tosão de Ouro, a Placa de Grã-Cruz da Ordem de Carlos III, a Placa da Ordem de Nossa Senhora da Conceição de Vila Viçosa, e respectivas faixas. Segura na mão esquerda uma bengala.
Palácio do Correio Velho
Oct. 25, 2022
ATTRIBUTABLE TO DOMINGOS ANTÓNIO DE SEQUEIRA (1768-1837), SKETCH FOR ALEGORY
Est: €1,000 - €1,500
ATTRIBUTABLE TO DOMINGOS ANTÓNIO DE SEQUEIRA (1768-1837), SKETCH FOR ALEGORY Charcoal and gouache on paper. Dim.: 41x49 cm.
Renascimento
Jul. 20, 2022
DOMINGOS SEQUEIRA, Desenho a sépia, 16 x 26 cm.
Est: €400 - €600
DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Desenho a sépia sobre papel Assinado e datado de 1798 Dim. aprox.: 16 x 26 cm. Manchado e amachucado. Emoldurado (defeitos).
Palácio do Correio Velho
Jul. 20, 2022
DOMINGOS SEQUEIRA, Desenho, 26x21 cm
Est: €200 - €400
DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Figura masculina Desenho colorido sobre papel Assinado Dim. aprox.: 26 x 21 cm. Papel amarelado e manchado. Emoldurado (defeitos).
Palácio do Correio Velho
Jul. 19, 2022
DOMINGOS SEQUEIRA, Desenho s/papel, 26,5 x 37,5 cm
Est: €400 - €800
DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Putti Desenho sobre papel Assinada "Seq.ª inventou e desenhou" Dim. aprox.: 26,5 x 37,5 cm. Papel amarelado com manchas de humidade. Verso com etiqueta com dados sobre a obra. Emoldurado (defeitos).
Palácio do Correio Velho
Jun. 27, 2022
DOMINGOS SEQUEIRA (1768-1837), HEAD OF A GIRL
Est: €600 - €900
DOMINGOS SEQUEIRA (1768-1837), HEAD OF A GIRL Brown shades wash on paper. Signed. Thornbush and Brazilian rosewood frame. Dim.: 19.3x15 cm.
Renascimento
Jun. 27, 2022
DOMINGOS SEQUEIRA (1768-1837), OLD MAN
Est: €300 - €500
DOMINGOS SEQUEIRA (1768-1837), OLD MAN Pencil and pastel on paper. Signed. Thornbush and Brazilian rosewood frame (small defect). Dim.: 20.5x27 cm.
Renascimento
Jun. 06, 2022
DOMINGOS SEQUEIRA - 1768-1837, "Moeda de César", oil on canvas, relined, restoration, unsigned, Dim.
Est: €45,000 - €67,500
DOMINGOS SEQUEIRA - 1768-1837, "Moeda de César", oil on canvas, relined, restoration, unsigned, Dim. - 72 x 94 cm
Cabral Moncada Leilões
Mar. 28, 2022
DOMINGOS SEQUEIRA - 1768-1837, Portraits of Maria Joaquina Rodrigues de Sampaio and José Joaquim Rod
Est: €1,000 - €1,500
DOMINGOS SEQUEIRA - 1768-1837, Portraits of Maria Joaquina Rodrigues de Sampaio and José Joaquim Rodrigues de Bastos, charcoal and white pencil on paper, gilt frames, moisture stains and minor faults in the support, frames with minor defects, one of them signed and dated 1821, Dim. - 32 x 23 cm
Cabral Moncada Leilões
Nov. 11, 2021
DOMINGOS SEQUEIRA (1768-1837)
Est: €800 - €1,600
DOMINGOS SEQUEIRA (1768-1837) "Figuras" Carvão sobre papel, assinado. Pequenos defeitos, manchas. Dim: 18,5x27,5 cm.
Corte Real, Leiloeira
Sep. 29, 2021
Crucified Christ
Est: €5,000 - €8,000
Oil on canvas
Veritas Art Auctioneers
Sep. 29, 2021
Portrait of João Carlos de Saldanha (First Duke of Saldanha)
Est: €1,000 - €1,500
Charcoal and chalk drawing on paper ca. 1827
Veritas Art Auctioneers
Sep. 29, 2021
Ugolino and His Sons
Est: €100 - €150
Black print on paper Portugal 19th/20th century (some spotting)
Veritas Art Auctioneers
Sep. 29, 2021
A study
Est: €100 - €150
Sanguine on paper
Veritas Art Auctioneers
Sep. 29, 2021
A study for allegory
Est: €600 - €800
Charcoal and chalk drawing on blue charcoal
Veritas Art Auctioneers
Sep. 29, 2021
A study
Est: €200 - €300
Pencil drawing on paper
Veritas Art Auctioneers
Sep. 27, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €800 - €1,200
DOMINGOS SEQUEIRA - 1768-1837, Calvary, Indian ink and watercolour en grisaille on paper, some browning on the support, signed. Notes: Cabral Moncada Leilões registers and thanks Dr. Alexandra Markl for her availability and both confirmation and information about this work., Dim. - 31 x 19 cm
Cabral Moncada Leilões
Sep. 27, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €1,500 - €2,250
DOMINGOS SEQUEIRA - 1768-1837, Study for portrait of lady with child, charcoal and white chalk on paper, moisture stains and some browning on the support, unsigned, back with handwritten inscriptions attributing to the Author and information PURCHASED FROM THE PEREZ COLLECTION (?), Dim. - 27 x 21 cm
Cabral Moncada Leilões
Sep. 27, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €2,000 - €3,000
DOMINGOS SEQUEIRA - 1768-1837, Studies of People and Movements for the "Allegory to the Promulgation of the Constitution of 1822" and the Figure of Camões for "A morte de Camões", charcoal and white chalk on both sides of the same paper, together with four print proofs of the aforementioned drawings by Domingos Sequeira for the booklet "The reconstitution of a lost painting", by LUIZ XAVIER DA COSTA (1871-1944), some foxing on the support, unsigned, Dim. - 41 x 26 cm
Cabral Moncada Leilões
Sep. 27, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €700 - €1,050
DOMINGOS SEQUEIRA - 1768-1837, To Caesar what is Caesar’s and to God what is God’s, Indian ink and watercolour en grisaille on paper, small restoration, minor faults and defects on the support, unsigned. Notes: Cabral Moncada Leilões registers and thanks Dr. Alexandra Markl for her availability and both confirmation and information about this work., Dim. - 18,5 x 23,5 cm
Cabral Moncada Leilões
Sep. 27, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €800 - €1,200
DOMINGOS SEQUEIRA - 1768-1837, Allegory to Time, Indian ink and watercolour en grisaille on paper, handwritten inscription "Em Memória do dia 22 de Julho do Anno de 1811 - Ill[ustrissi]mo Ex[celentissi]mo S[enh]or Conde de Redondo Thomé Joze D'Souza Coutinho", minor defects on the support, signed and dated 1811. Notes: Cabral Moncada Leilões registers and thanks Dr. Alexandra Markl for her availability and both confirmation and information about this work., Dim. - 16,5 x 14,5 cm
Cabral Moncada Leilões
Jul. 05, 2021
DOMINGOS SEQUEIRA - 1768-1837
Est: €3,000 -
DOMINGOS SEQUEIRA - 1768-1837, Untitled, charcoal on paper, small restoration, unsigned. Notes: source: former collection of Viscount da Lançada, D. Alexandre de Sousa Holstein., Dim. - 33 x 26 cm source: former collection of Viscount da Lançada, D. Alexandre de Sousa Holstein.
Cabral Moncada Leilões
May. 24, 2021
DOMINGOS SEQUEIRA (1768-1837), "OS ÚLTIMOS MOMENTOS DE CAMÕES"
Est: €400 - €600
DOMINGOS SEQUEIRA (1768-1837), "OS ÚLTIMOS MOMENTOS DE CAMÕES" Charcoal and chalk, inscriptions in the back. Study for the painting presented in Paris in 1824, today considered lost. Framed. Provenance: Marquis of Sousa Holstein, Manuel Braga São Romão, Dr. Luiz Augusto de Oliveira (Viana do Castelo) and Dr. Luiz Xavier da Costa. Dim.: 25x34 cm.
Renascimento
Apr. 15, 2021
Head of a Old Woman
Est: €3,000 - €5,000
Oil on canvas
Veritas Art Auctioneers
Feb. 19, 2020
DOMINGOS SEQUEIRA, Desenho s/ papel, 27 x 21,5 cm.
Est: €200 - €400
Atribuído a DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Estudo de figuras Desenho a sépia sobre papel Não assinado Dim. aprox.: 27 x 21,5 cm.
Palácio do Correio Velho
Feb. 19, 2020
DOMINGOS SEQUEIRA, Desenho s/ papel, 36 x 29,5 cm.
Est: €3,000 - €5,000
Atribuído a DOMINGOS SEQUEIRA, Domingos António de Sequeira (1768-1837) Estudo para cena religiosa Desenho a tinta e lápis sobre papel Não assinado Dim. aprox.: 36 x 29,5 cm.
Palácio do Correio Velho
Dec. 10, 2019
DOMINGOS SEQUEIRA (1768-1837), "A MORTE DO CONDE UGOLINO"
Est: €150 - €250
DOMINGOS SEQUEIRA (1768-1837), "A MORTE DO CONDE UGOLINO" Depicting Count Ugolino in prison, surrounded by three of his children. Engraving, after Sequeira, before 1859 (original drawing belongs to the National Museum of Ancient Art - Lisbon, no. 2695). Edition for the readers of "Revista Contempo-ranea de Portugal e Brazil", Lisbon, 1862. Framed. Some spots. Dim.: 28x38.5 cm.
Renascimento
Oct. 07, 2019
SEQUEIRA, Domingos Antonio de (1768-1837) Vieil homme assis : portrait du poète Luís Vaz de Camões pierre noire, craie blanche, estompe sur papier gris 13,9 x 13,2 cm. (5 3/8 x 5 ¼ in.)
Est: €1,000 - €1,500
SEQUEIRA, Domingos Antonio de (1768-1837) Vieil homme assis : portrait du poète Luís Vaz de Camões avec inscription 'Estudo de quadro (Camões)' (verso du cadre) pierre noire, craie blanche, estompe sur papier gris 13,9 x 13,2 cm. (5 3/8 x 5 ¼ in.)
Christie's
Sep. 23, 2019
Saint Joseph's death
Est: €3,200 - €4,800
DOMINGOS SEQUEIRA - 1768-1837, Saint Joseph's death, sanguine on paper, signed, small defects on the paper, Dim. - 45 x 37 cm
Cabral Moncada Leilões
Oct. 03, 2018
DOMINGOS SEQUEIRA (1768-1837) (Attribution) - 'Five Faces'
Est: €600 - €800
DOMINGOS SEQUEIRA (1768-1837) (Attribution) - 'Five Faces' China ink on paper, signature. Dim .: 16x21,5cm.
Marques dos Santos
Sep. 26, 2018
DOMINGOS SEQUEIRA (1768-1837), "DISCURSO SOBRE A COMIDA" (SPEECH ON FOOD)
Est: €500 - €800
DOMINGOS SEQUEIRA (1768-1837), "DISCURSO SOBRE A COMIDA" (SPEECH ON FOOD) Pencil on paper. Signed. No. 155 on drawing and title in the back. Miniature drawing. Dim.: 5.3x9.6 cm.Domingos Sequeira was one of the most important artists in Portugal in the early 19th Century.
Renascimento
Jul. 11, 2018
DOMINGOS SEQUEIRA (1768-1837) (attributed) - 'Death of Caesar'
Est: €2,250 - €3,000
DOMINGOS SEQUEIRA (1768-1837) (attributed) - 'Death of Caesar' Oil on canvas, signed on the back: Dim: 37.5x48 cm.
Marques dos Santos
May. 28, 2018
"Missiva ao Marquês de Marialva" (Letter to the Marquis of Marialva)
Est: €2,000 - €3,000
DOMINGOS SEQUEIRA - 1768-1837, "Missiva ao Marquês de Marialva" (Letter to the Marquis of Marialva), pen drawing on paper, moisture stains, acidity spikes, minor fault on the paper, not signed, Dim. - 30 x 21 cm
Cabral Moncada Leilões
Nov. 09, 2017
DOMINGOS SEQUEIRA (1768–1837), CLASSICAL SCENE
Est: €400 - €600
DOMINGOS SEQUEIRA (1768–1837), CLASSICAL SCENE pencil drawing on paper, miniature style. Signed. Inscriptions on the back. Dim.: 6.6x9.2 cm.
Renascimento
Dec. 31, 2016
Domingos Antonio de Sequeira (1768-1837)
Est: €100 - €130
Domingos Antonio de Sequeira (1768-1837) Album with a set of eight reproductions. One extra Monumental edition. Original fold and pertaining documentation. Dim.: 53.0 x 43.5 cm Dim.: 56.0 x 46.0 x 3.0 cm
P55 - Second Hand Luxury
Jul. 07, 2016
DOMINGOS SEQUEIRA (1768-1837) (assignment) - 'Study'
Est: €900 - €1,200
DOMINGOS SEQUEIRA (1768-1837) (assignment) - 'Study' Pencil on paper. Preparatory study for painting. Dimensions: 19x26 cm.
Marques dos Santos
Jul. 07, 2016
DOMINGOS SEQUEIRA (1768-1837) (assignment) - 'Study'
Est: €900 - €1,200
DOMINGOS SEQUEIRA (1768-1837) (assignment) - 'Study' Pencil on paper. Preparatory study for painting. Dimensions: 25x34 cm.
Marques dos Santos