Apollo in the Forge of Vulcan

The subject is taken from Roman mythology, specifically from Ovid's Metamorphoses. Velázquez interpreted the scene into a strictly human version, with contemporary figures. Apollo is seen wearing a toga which leaves his torso exposed to view. Vulcan, in this picture, is just a blacksmith, as are his helpers, who are men from the village who know the trade. Vulcan is staring at him in astonishment after having heard the news of his wife's adultery with the god Mars, for whom he is forging armour at this very moment. The cave in which the blacksmith god forges weapons for the other deities in this painting is shown as a smithy, similar to those Velázquez could have seen in Spain or in Rome. With characteristic mastery Velázquez also painted a variety of objects which would be commonly found in a forge.

Velázquez interest in nudes is not surprising, and evidence of this appears as early as his arrival in Madrid in 1623, although the appearance of them in his works increased after his first visit to Italy in the years 1629–1631.

During his Italian journey he was also influenced by Venetian painting, which can be seen in his use of colour, for example in Apollo's striking orange tunic. From his travels through Rome he was influenced by Michelangelo to create extremely large and strong figures. The musculature of Vulcan and the other figures that surround him is not insignificant; they are athletic figures who show off their strength without modesty, even standing in positions that show off their muscles to greater effect.

On the other hand, Velázquez was always obsessed with achieving depth in his works. In this case he started to use what is known as "space sandwiching", that is, putting some figures in front of others so that the sensation of depth exists in the viewers' minds. In this way he portrays depth, rather than just using the view through the window seen at the back of the room. As in many of his works, the photographic quality of the objects (mostly metallic: armour, the anvil, the hammers and the red-hot iron itself) that appear in the painting which show realism taken to the extreme. At the back, in the upper right, various objects can be seen on a shelf which form a still life by themselves, which is characteristic of Velázquez' early works.

As a Spanish painter his characters are ordinary people, not idealised as in Italian works. Vulcan could even be said to be quite ugly, and Apollo's face, despite being surrounded by an aura which differentiates him from the rest, is also not idealized.[5]

Part of pigments used by Velázquez in this painting[6] have changed their colours so the canvas lost its original color balance. The wreath of Apollo was originally painted green by mixing (blue) azurite, yellow lake and yellow ochre. The lake pigment is not very stable and so the present color of the wreath is almost blue. The color of the loin cloths changed to flat dark brown while the flesh colour mainly containing yellow ochre, vermilion and azurite remained unchanged.[7]