Question: What medium was The Last Supper painted in?
About the article "Leonardo da Vinci", section "Paintings of the 1490s".

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 Name of project/picture: The Last Supper Claimed by: HAL9000 Srl - Novara - Italy Photograph of: "The Last Supper", as painted by Leonardo da Vinci, in the back halls of the dining hall at Santa Maria delle Grazie in Milan, Italy.
Dimensions: 172,181px (W) × 93,611px (H) Size: 94.4 GB Pixels: 16,118,035,591 Year: 2007 The Last Supper (2007).
The 16.1 Gigapixel size was reached by HAL9000 Srl.
The project "The Last Supper" was claimed to be the largest digital panoramic photo.
It is a stitched photograph created merging 1677 shots from a single point into one photograph, each shot 12.2 Megapixel in size. 
While certainly a representation of diners in Arles (regardless of the cafe), in his article "Van Gogh's Last Supper: Transforming "the guise of observable reality,"" Baxter argues this is van Gogh's initial attempt in creating a Symbolist or "sacred realism" "Last Supper":Although Hulsker argued that determining whether this or its sister painting came first would be speculation, Baxter offers the following argument: the second version is painted in a Cloisonnist style, giving it a stained glass window effect, a suitable medium for a "Last Supper" painting; and van Gogh has made a number of changes to the final version, most notably: adding bread and placing a new wine bottle before the central serving figure, giving it emphasis.
Furthermore, van Gogh added more diners, including the figure hiding behind, what was once a vase of flowers, now appears to be a palm frond.
Also, the flower arrangement on the left now resembles the top of a poll axe and is at about the same position where Simon Peter wields a blade in Leonardo da Vinci's version.
But most importantly, right next to it, van Gogh has replicated Leonardo’s leaning image of the apostle John, van Gogh’s favorite.
Finally, van Gogh has enframed a female serving figure within vases of flowers, a motif he would return to months later with his "Berceuse" triptych.
And lastly, all the empty chairs, which can be immediately recognizable from "Vincent’s Chair", also his "Bedroom in Arles", and he’d just bought twelve to furnish the Yellow House literally hours before beginning his final Symoblist's "Last Supper" Café Terrace at Night 
In 1447 he worked in the refectory of Sant'Apollonia in Florence, painting, in the lower part, Last Supper fresco, accompanied by other scenes portraying the Deposition, Resurrection, and Crucifixion, which are now damaged.
He also painted a lunette in the cloister, depicting a "Pietà".
The "Last Supper" displays del Castagno's talents at his best.
The detail and naturalism of this fresco portray the ways in which del Castagno departed from earlier artistic styles.
It is likely that Leonardo da Vinci was already familiar with this work before he painted his own Last Supper in a more dramatic form to contrast with the stillness of these works, so that more emotion would be displayed. 
Cristobal López (18th century) (died 1730) was a Spanish painter.
He was the son of Josef Lopez of Seville, and Cristobal painted largely for the South American market, and painted in fresco in the church of All Saints, a giant "St. Christopher" and a "Last Supper". 
The Last Supper (1480) is a fresco by the Italian Renaissance artist Domenico Ghirlandaio.
It depicts Jesus and the Apostles during the Last Supper, with Judas sitting separately on the near side of the table, as is common in depictions of the Last Supper in Christian art.
Ghirlandaio was already famous and was about to travel to Rome to paint the Sistine Chapel with other Florentine painters when he received the commission for this fresco.
During the restoration of the fresco later, a preliminary sketch of it was discovered on the left wall of the refectory in Cenacolo di Ognissanti.
It is likely that Leonardo da Vinci was already familiar with Ghirlandaio's treatment of the Last Supper, as well as that of Castagno, and painted his own Last Supper in a more dramatic form to contrast with the stillness of these works, so that more emotion would be displayed.