[This is the fourth in the series of articles I would be posting on the art of painting in ancient India with particular reference to the Chitrasutra of Vhishnudharmottara purana
The previous (third) article dealt with the physical features of various classes and types of images, proportions, projections, foreshortening etc. covered certain concepts and general aspects discussed in Chitrasutra.
The current article is about colours; the concepts, classifications and application of colours. It also briefly mentions about shading and how to go about drawing.]
13.1. Chitrasutra in one of its passages observes that delineation, shading, ornamentation and colouring are the decorative aspects of a painting; suggesting that rekha the lines that articulate the forms are the real substance of a painting.
At another place, the text remarks, “The masters praise the rekhas –lines (delineation and articulation of form), the connoisseurs praise the display of light and shade, women like the display of ornaments,; and , the richness of colours appeals to common folks.”
Rekham prasamsaniya -acharya; vartanam apare jaguh / striyo Bhushanam ichchhanti; varnadhyam itare janah // 3.41.11
13.2. Yet, the colors are very important and significant aspects of a painting; they enliven a depiction. The text says , ” when a learned and skilled artist paints with golden( radiant) color, with articulate and yet very soft lines with distinct and well arranged garments; and graced with beauty, proportion , rhythm and inspiration, then the painting would truly be beautiful.”
13.3. The six limbs (anga) of painting enumerated in the text include Varnika-bhanga, which represents the artistic manner of improvising colour combinations, tones and shades. It provides for infusion of emotion, creation of lustre and irradiance. That involves, among other things, delicate and skilful use of brushes and other aids. It represents the maturity of the artist’s techniques and fruitfulness of his experience
Colour, therefore, is a major medium in painting; the emotions and moods are expressed through manipulating colours, their density, tones, lines, light, shades etc. The ingenuity, imagination and skill of the artist discover their limitations here.
13.3 While the Sutra-pata-rekha is the first line of the outline, the subha-varti-rekha is the finished sketch, ready for taking the colors. Now is the time for mandala – karya, drawing of curves, characterized as manorama (charming) and askhalita (un -erring) is the final stage of subha-varti-rekha. In this stage, the initially blocked rough contours are carefully rounded off at their edges; and, a new grace is added to the figures by more definitive work.
The initial coat of color is to be light (virala vilepana) and only the later depths are suggested by Vartana.
13.4 . The term Varna-krama indicates the general arrangement of color-scheme in a painting, the balancing of the tints to achieve a color-harmony. That term is also said to indicate the laying of tints like green, yellow and the rest (varnakramo harita, pita adi varna-vinyasah). Another term, varna-sthiti – is meant to indicate the color laid in its proper place in the picture. Such placement of just the right color in just the right place on the canvas is considered very essential, at least in the preliminary stages of coloring, when the effect of one color over the other, their contrast, the balance, the tone and such other details are to be determined.
The refinements of touching and blending etc. might come in later at proper time and place.
14. Colour – symbolism and suggestions
14.1. The colors in a painting have a descriptive and also a suggestive significance. Colours bestow a personality to a figure and speak eloquently of its character and mood. Colours also carry rich symbolism; they might depict the gunas such as the satva, rajas or tamas; and make explicit the essential character and attributes of an image.
In certain Vasishnava traditions , Radha the personification of love and beauty, is adorned in the colour dearest to her, the enchanting blue of Krishna, while he is clad in pitambara the lustrous golden hue of his beloved Radha, signifying sanidhya , the sense of being ever together.
There was, in addition, a class of pictures called rasa-chitra, the pictures of emotions, also called varna-lekhya meaning interpretations through colour. These were different from realistic paintings and sought deliberately to represent various emotions through distinct colours. In this school, idioms of colour visualized a range of emotions; and, each rasa had to be portrayed in its uniquely expressive colour. For instance:
- Srinagar (erotic) was of shyama hue(light sky blue) ;
- hasya (that which evokes laughter) in white;
- karuna (pathos) in gray;
- raudra , (the furious) in red;
- vira (the heroic) in yellowish-white;
- bhayanaka (the fearsome) in black;
- adbhuta (supernatural and amazing) in yellow ; and
- bhibathsa (the repulsive ) in blue colour.
14.2. The colours of our mythological figures represent, symbolize and convey their attributes. For instance, the highest divinities with supreme attributes (gunas) are sky blue signifying their true infinite nature; Shiva, the ascetic the supreme yogi is Gauranga; he is colourless and almost transparent, he is without any attributes; Hanuman and Ganesh are red like the blood; full of energy, vitality and life; and Kali’s black does not signify absence of colour but is the sum and culmination of all colours and energies in the universe. Her black is endowed with limitless powers of attraction that draws into her the entire existence.
14.3. During the later periods, the Ragamala School of painting attempted translating the emotional appeal of a Raga into visual representations. Each raga was personified by a colour, mood, the nature surrounding the hero and heroine (nayaka and nayika). It also elucidated the season and the time of day and night in which a particular raga is to be sung. The colours, substance and the mood of the Ragamala personified the overall bhava and context of the Raga. It is a delightful amalgam of art, colour, poetry and music.
II. Colour in Chitrasutra
15. Primary colours and their derivatives
15.1.Talking of colors; Chitrasutra mentions basic colors as five, while the others only four (red, yellow, blue and white); though both agree on white as a primary color.
Chitrasutra, in chapter 27, mentions five primary colours (mulavarna) : white (svetha), yellow (pitha) , black (krshna), green (harita) and red (raktha).
Mula-rangaha smruthaha pancha, Shewtaha Pitha vilomathaha / Krishno Nilash cha Rajendra shatha shontaraha Smurtha /
raktas tatha pitah krishno harita eva cha, mulavarnas samakhyatah panha parthivasattama, ekadvitrisamayagat bhavakalpanaya tatha, sankhyaivantaravarnanam loke kartum na sakyate.
The idea of four colors with yellow composed of gorochana; white sandal, crimson saffron; and dark musk in the varied hues of gems like turquoise, diamond, ruby and amethyst.
Pita vadata arunanilabhasam deho padehotkiranair maninam / gorochana-chandana-kumkumai-nana-abhivilepanam punruktayantim / /
At another place (ch.40) it mentions white, yellow, black, blue (shyama) and the colour of myrobalan (the dried fruit of a bush that resembles a plum) as the five principal colors.
15.2. The text says , it would be impossible to enumerate the mixed colors in the world created by the dexterous mixing of various colors and their derivatives; the combinations are limited only by ones imagination and logic. The mixing of two or three colors, in various shades and tones, and their manipulation is a mark of artist’s ingenuity. There is no limit to the numerous finer varieties of tints that can be produced by the imagination of the artist. Coloring should , however, be natural.
It appears, the range of colors employed by the ancient artists was wide enough to render with subtlety the local colors of the objects.
The mixing of these colors is left to the of the ingenuity of the artist. He may coat them with lac and resin. Coloring substances are : gold, silver, copper, mica, deep coloured brass, red lead, vermilion, tin, yellow orpiment, yellow myrobalan, lac, indigo and some kind of iron oxide.
[Prof. Beni Madhav Barua points to a passage in the Samyutta-Nikaya (Part III, p. 152) , where the Buddha ,incidentally, mentions the following vegetable substances used by the dyers or painters for preparing dyes or colours ; (1) resin (rajana); lac (lakha); turmeric (balidda); indigo (nili);and, madder (manjetthi).]
15.3. Chitrasutra classifies the application of colours into four categories: as those that are employed to depict :
- (i) the faithful representations of nature;
- (ii) the true proportions but largely exaggerated size of the object;
- (iii) artificial qualities and perspectives of objects; and,
- (iv) an admixture of the three.
15.4. The text mentions five kinds of whites of light shade (gaura); and twelve kinds of whites of dark shades (shyama). The light -whites are the :
- gold like white (rukma) ;
- ivory like white (danta-gauri);
- white like the split sandal(sphuta-candana-gauri);
- autumn cloud like white( sharada- ghana) ; and
- autumn moon like white (sharad –candraka- gauri).
Some other texts, which followed Chitrasutra give a slightly varied versions of the light -whites as: milk, pearl, silver, star or a conch-shell (Kasyapasilpa); Foam-white, champaka and karnikara flowers (Bana); and lime (Manasollasa).
15.5. The twelve types of dark (shyama) shades of white which are derived by the mixtures and manipulations of white with other colors and shades, as mentioned in the text are:
- the mixtures with dark red (raktha-shyama);
- with brownish red like the mudga pulse (mudga-shyama);
- with dark green like durva grass (durvankura-shyama);
- with pale green (pandu-shyama);
- with greenish like topaz (harita -shyama);
- with yellow (pitha-shyama);
- with brown like priyangu creeper (priyangu- shyama);
- with reddish brown like monkey’s face (kapi -shyama);
- with blue like blue lotus (nilothpala -shyama);
- with slight blue like casa bird (casa- shyama);
- with purple- lotus – red (raktotpala-shyama) ;
- and , with grey- dark like a dark cloud (ghana-shyama).
The objects gain a character (vishesha) and a dimension with judicious inter-mixture of colors.
15.6. The text then goes to describe the forms of a few other colours.
Blue colour is said to be of three kinds: with white predominating, with very little white; or with both in equal parts.
When blue is transformed a great deal it becomes green; and, it could be pure green or an admixture of white; and green with blue predominating. Blue with black and red becomes metallic blue (nila-lohitha). Blue is transformed variously while in association with anything applied as an astringent.
Blue tinged with yellow and white gives rise to a variety of colours and shades; and to Blue- lotus colour when shaded dark.
“Thus beautiful paintings should be made greenish like durva sprout; Yellowish like wood-apple; and dark like mudga.”
The kinds of red mentioned in Manasollasa and Kasyapasilpa are :
- red lead (darada),
- crimson (sona),
- juice of lac (alaktarasa),
- blood red (raktha),
- soft red (mridu-raktha), and
- red ochre (lohita).
“A painting in red and dark like the red-lotus (rakthothpala)
becomes beautiful when combined with white lac, covered by a coating of lac and resin.”
Four kinds of yellow are mentioned in Kasyapasilpa:
- golden (svarna),
- yellow (pita),
- turmeric (haridra) and
- like pollen of lotus (pisanga ).
As regards black, Kasyapasilpa mentions four shades:
- of clouds (nila),
- of forest crow (shyam),
- of a peacock (kala) , and
- of wing of a black-bee (krshna)
To that list Bana adds :
- light black like that of a buffalo;
- darker black like the face of a golangula monkey;
- black of the pitch dark night.
“By proper selection and distribution of colours a painting becomes beautiful.”
“A painting should be then very beautiful, when a learned artist paints it with golden colours, with articulate and yet very soft lines, with distinct and well arranged garments ; and blessed with beauty of proportions and rhythm.”
16. Colour pigments
The colour pigments were made from mineral and vegetable colouring substances (Rangadravyas) or dyes.
16.1. The text mentions some colouring articles :
- gold (kanakam ) ,
- silver (rajata),
- copper (tamra),
- mica (abrakam ),
- lapis lazuli’s (rajavarta),
- red lead (sindhura),
- lead (tavara),
- yellow orpiment (haritala- a bright yellow arsenic sulphide mineral),
- lime (suddhe),
- lac (lakshya),
- vermillion (hingulakam) and
- indigo (nila).
Rangadravyani kanakam rajatam tamram eva cha abhrakam rajavartam cha sinduram trapur eva cha, haritalam sudha laksha tatha hingulakam nripa, nilam cha manujasreshtha tathanye santyanekasah, dese dese mahaaja karyas te stambhanayutah, lohanam patravinyasam bhaved vapi rasakriya- 3. 40. 25-27
It is said; in case of all colors the liquid of sindhura tree is desirable.
16.2. The text further says:
“In every country, there are many such substances. They should be manufactured with an astringent (stambhanayutah). The irons or metals should be either thinned into leaves (patravinyasa) or they should be made liquid (rasakriya) – by chemical treatment. A mica defile placed in iron should serve as a distiller. In this way, iron becomes suitable for painting”
[There is also a reference to dying the cloth with varied figures. Not only were paintings made of cloth but the cloth itself was dyed so as to be decorated with figures. It is a technique for which, later , was made famous by the weavers of coastal Andhra Pradesh.]
16.3. The Gold sheet and powder was used to make the background or details in painting. Gold is of the most malleable and softest of metals. Therefore, it can be made in to a very thin sheet and cover wide surfaces. There were various methods for the preparation of powdered gold.
There is an interesting description of the process of turning gold into gold-paint. The text says:
“Pure gold, which is costly, should be slowly ground on a stone slab with an instrument (tunda) having at its tip the virana grass.
The gold-powder thus prepared should be placed in a bronze vessel and melted over again. Thereafter water should be poured into it and then be stirred up time and again. Now water of the vessel should be so carefully shifted that the stone-dusts remain for their solidarity. In this manner, pure golden pigments, showing the hue of the luster of a newly risen sun, would be prepared.
Thereafter, this gold-pulp should be mixed with a small quantity of vajralepa, should be placed at the tip of the brush and all ornaments, imagined as of gold, should be gilded therewith. When the gold applied in painting becomes dry, it should be slowly rubbed with a boar-tusk as long as necessary to attain a brightness of lightning.”
“A painting should be then very beautiful, when a learned artist paints it with golden colors, with articulate and yet very soft lines, with distinct and well arranged garments; and blessed with beauty of proportions and rhythm.”
The Shilparatna (1.46.124-132) mentions two systems for application of gold on to the painting: one, with gold powder mixed with vajralepa; and, the other with gold leaves.
The first method requires that before grinding gold, it should be turned into thin and soft leaves; and, those leaves should be very minutely fragmented and mixed up with small quantity of sand and clean water. And, thereafter, it should be mixed with water and poured into a pot, which should then be well shaken, so that the sand will rise above the gold, which is heavier. After removal of dirt and sand, the gold would shine very bright. And, that gold should be pasted along with proportionate glue (vajralepa) ; and , skillfully applied with a suitable brush. When dried up, it should be slowly rubbed with the tip of boar-tusk till the gold glitters.
As per the second method, the spots on the painting meant for gliding should be smeared with glue; and, extremely thin gold leaves should be laid thereon very steadfastly. Again, the gold-spots should be brightened by rubbing.
17.1. Methods of producing effects of light and shade were considered very important for projecting three dimensional presentation of the image.* Weakness or thickness of delineation, want of articulation, improper juxtaposition of colors are said to be defects of painting.”
One of the endearing features of Ajanta art is shading the different parts of the body to produce three dimensional effects in the images. The other was use of proper colors at times contrasting and at times matching to create magical effects. These were precisely the principles that Chitrasutra emphasized.
The Shilparatna (1.46.113-117) explains that a skilled painter should fill in colors slowly and spotlessly with a flat brush in order to achieve the three-dimensional special effects of depressions and protrusions. Everything should be made to appear pleasing by differentiation of darkness and brightness; and, of hardness and softness. In application of individual colors, the effect of thickness is dark; and, that of thinness is bright. This effect is also achieved by using different colors. Where yellow stands for bright; red would be dark. The borderline should be carefully drawn in lampblack (kajjala-varna) with a fine brush.
17.2. The text mentions three methods of Vartana-krama or delineation of depth on a flat surface by the suggestion of light and shade. Such effects are sought to be achieved by one or more of the techniques: Patraja (cross hatching); Binduja (stipping) and Rekhika (fine lineation).
Tisrascha Vartanah proktah patra-rekhika-bindujah ( 3.41.5)
The first method of shading (Vartana) is called (Patraja) on account of lines being in the shape of leaves. The Binduja method is restrained (i.e., not flowing) handling of the brush while planting dots patiently. And, the Rekhika method is said to be very fine line-shading
17.3. While stressing the importance of proper shading of an image the text mentions that a painting in which an object is devoid of shading (varttana) is of average class (madhyama). A picture which in some parts are shaded and the rest is un-shaded is below average or is bad (adhama). And, a picture shaded skilfully all over is best (uttama).
“A painting in which everything is drawn in an acceptable form in its proper position , in its proper time and age becomes excellent, while in the opposite case it becomes quite different.”
“A painting drawn with care, pleasing to the eye, thought out with supreme intelligence and remarkable by its execution, beauty, charm, taste and such other qualities, yields desired pleasure.”
[The murals at Ajanta, which were rooted in the principles of the Chitrasutra, are said to have influenced the Chinese painting techniques, particularly with regard to the style of depiction and shading; giving a three-dimensional effect to the details in the painting .
“The Indian Painting Technique introduced from India is also called the concave and convex method. The concave and convex method is one of the traditional painting techniques of India. The concave and convex method was widely used in the murals of the Ajanta Caves in India. This method in Indian traditional paintings was also introduced in China across central Asia, which is called “Indian Technique” in Chinese painting history.
The Chinese scholar Xiang Da said, “Both Indian and Chinese paintings give priority to the lines. But Indian painting adds the concave and convex method in the lines to present a three dimensional sense in a flat surface. For the figures painted, such as the arms, contour lines are clean and lively, deep colours are added along the lines, which change gradually to soft and light internally, forming a round shape. This is what is called the concave and convex method. The Ajanta and Sigiriya Caves in Ceylon (now Sri Lanka) all used this method to show light and shade. The Indian painting was introduced in China; the most notable and worth praising part of it is also this concave and convex method, going in the same channel of western painting introduced in China in Ming and Qing Dynasties.”
18. Brushes and crayons
The text mentions the tools required for drawing and sketching. Vartika was a general term used to denote both a brush and a crayon or a pastel for drawing. The Chitrasutra suggests that brushes could made of hairs collected from the ear of a calf; from the belly of a goat; from the tail of muskrat; or from tips of grasses.
It appears Tindu was a crayon too, of carefully burnt ebony twig; while kitta was black carbon prepared as a roll for sketching. Tulika was brush prepared, perhaps, out of animal hair like sable, squirrel and hog; and , of bird feathers. It is said; a painter used at least nine brushes for every color.
The text says, “A painting firmly drawn with a tulika , a magnificent hairy brush , on a canvas dipped in juice of the best Durva grass cannot be destroyed ; and it remains intact for many years , though washed by water.”
Eberhard Fischer in his paper The Technique of Indian Painters A short note observes :
It may also be of interest to mention that the fine brushes used by the Indian masters for precise lines are made from squirrel hair. The tied-together hair bushel cut from the tail is pulled through a bird’s feather quill and fixed to a bamboo handle. For each color, a separate brush is usually used. The finest brushes for outlining do not end in a straight tip but are considered best when the hair possesses a natural sickle-like curve ending in a tip. With this peculiar brush, a master can draw a circle with an utmost uniform thin line! One should also not forget that Indian painters traditionally sit on the floor when working and keep the tablet with the picture on their left thigh. (When a low table is used its top is generally slanted at an angle.) The painter’s hand with the brush touches or even rests on the picture, which is covered at that point with a small piece of paper. The regular viewing distance is thus given by the length of the arm. The traditional miniaturist has his pigments mixed with gum Arabic (from the babul or acacia tree) and sometimes with catechu sap or with shellac for an even flow. Mixed pigments are usually stored in small river-mussel shells placed to the right of the painter on the ground.
19. How to go about the task?
The first requisite for a painting , of course, is bhu-labha or bhu-lambha the preparation of a proper, smooth, white surface to paint. It could be a canvas (pata), board (phalaka) or a wall (bhitti).
In the process of preparing the ground and then in fastening colors on that ground, the binding medium plays a very significant role in painting.
In fact, in the characterization of technique of a painting the nature of the medium is always taken into consideration; and accordingly, the universally accepted classification, such as, oil, water, tempera, fresco, etc. is generally formulated on the basis of the medium.
preparation of Bhumi: – preparation of board phalaka or canvas, pata, or ghattana – phalaka ghattinchi: is the preparation of the board with canvas applied to it; and, – Merungidi is ‘giving brilliance’.
In the case of canvas on a board, Sri Vidyaranya describes that process in his Panchadasi,
“yatha dhauto ghattitascha lanchhito ranjitah patah “-
‘like the canvas whitened, prepared, marked i.e. sketched out and colored….’
-As regards the preparation of wall: Bhitti- samakara , it is said : The preparation of loam to be applied to the plaster on the wall to make a proper base for painting is as follows: a mixture of powdered brick, gum resin, bees wax, molasses, oil, burnt lime plaster, in definite proportions, pulp of bilva, bark or pinhchhila, sand and lime all to be soaked for a month in water. The surface of the wall to painted on has to be prepared by the application of this loam, the coat neither too thick nor too thin, making it meticulously even in its surface and glossy, smoothened with clayey liquid, juice of sarja and oil and rubbed by repeated sprinkling of milk, so that when it is dry it could last a century.
[ For a detailed note on the subject of Paint grounds and binders according to ancient Sutras, please refer to the latter half of Part Four of this series.]
Sutra-pata-rekha are the very first lines of an outline of a preliminary sketch. The outline sketch is usually drawn a stump of a sort pencil called Vartika.
– purvam tinduka-lekhyam syad yad va vartikaya budhaih / aakara -matrikam rekham vina likhet punah //
This rough sketch seems to be called as varnaka or hastalekha.
The outline, no doubt, is a quickly drawn rough sketch. Yet, it is a well thought-out , meaningful , studied drawing.
While the Sutra-pata-rekha is the first line of the outline, the subha-varti-rekha is the finished sketch, ready for taking the colors. Now is the time for mandala – karya, drawing of curves, characterized as manorama (charming) and askhalita (un -erring) is the final stage of subha-varti-rekha.
In this stage, the initially blocked rough contours are carefully rounded off at their edges; and, a new grace is added to the figures by more definitive work.
The initial coat of color is to be light (virala vilepana) and only the later depths are suggested by Vartana.
The text briefly mentions how a painter should go about his task. The outlines ought to be drawn in yellow and red as a rule.
“The painter should think of the proportionate size of the thing to be painted, and think of it as having been put on a wall. Then calculating its size in his mind , he should draw the outline marking the limbs. It should be bright in prominent places and dark in depressed places . It may be drawn in a single color , where comparative distinction is required. If depressed places are required to be bright , jet black should be used . “
At another place, the text mentions that outlines should be drawn with un-oozing black and white brushes in due order fix them on the duly measured ground.
Outline has to be filled with the first colour-wash which could either white or green. And, it can later be filled with colour in appropriate places.
Chitrasutra cautions that an inconvenient painting stance or a bad seat or thirst or absentmindedness or sloppiness or bad temper could spoil the picture.
Dur-asanam, dura-nitam pipasa cha anya-chittaha / yete chitra-vinyasasya hetavaha pari-kirtitaha /3.41.13/
Sva anuliptva akasha nideshanam madhuka Shubha / su-prasanna abhi gupta cha bhumihi sat-Chitra-karmani /3.41.14/
Su-snigdha vispusta Suvarna -rekham vidvan anyata desha vishesha vesham / Pramana Shobha-birahiyamanam krutam bhaveth Chitram ativa chitram/3.41.15/
The text, Samarangana-sutradhara, mentions eight-limbs’ (asta-angani) of painting to which an artist should adhere for achieving success as a painter:
Bhumibandhana (preparation of surface) ; Vartika (crayon work) ; rekha-karma ( outline work ); laksana (features of face) ; varna-karma ( colorings ); vartana-karma (relief by shading ); lekha-karma (correction) and dvika-karma ( final outline)
Eberhard Fischer in his The Technique of Indian Painters A short note explains that Painting a picture is generally done in eight stages after the paper is burnished to make it compact, smooth and less absorbent:
1 The rough outline of the composition is sketched with charcoal.
2 The first drawing – often in sanguine – is done with the brush.
3 A first thin white wash is applied above this drawing.
4 The drawing is repeated, now in a thin but precise black line.
5 The white priming is laid over the drawing in such a thickness that its black lines remain feebly visible.
6 Before now filling in colors, excess pigments are erased with a sharp knife-blade, and the surface is burnished.
7 The pigments are laid – one by one – in thin layers, the first ones being a rather liquid wash and usually somewhat lighter than the final color. The picture is burnished from the back when dry, followed by a second round of applying pigments and burnishing.
8 When all colors are placed and dried, the outlines are traced, details incorporated and shading or volume indications done. Some wash with yellow or light brown may be given, gold can finally be applied on yellow undercoating, and white drops may be made for pearls from powdered conch shells or zinc oxide mixed with chalk. The gold (or tin for an silver effect) can be powdered foil and applied like other mineral pigments, but also gold leaf could be glued on the picture. In both cases its surface was often pierced with a blunt needle after burnishing it to enhance the glittering effect.
Sources and References:
I gratefully acknowledge Shri S Rajam’s sublime paintings
And other paintings from internet
Chitrasutra of the Visnudharmottara Purana by Parul Dave Mukherji
Stella Kramrisch: The Vishnudharmottara Part III: A Treatise on Indian Painting and Image-Making;
Second Revised and Enlarged Edition; (Calcutta University Press: 1928)
Technique of painting prescribed in ancient Indian Texts
The “Sarvatobhadra” temple of the Vishnu-dharmottara-purana