In Revelation 3:18, God advises the church in Laodicea to purchase eye salve from him, "so that you may see." In the context this has been explained as a metaphor for gaining spiritual sight and avoiding spiritual blindness, but the metaphor is based off of a well-known Roman practice.
A good deal is actually known about Roman "eye salve" (коλλоúριov). It is attested in numerous written sources, and a surprising amount is also known from archaeology. One of the interesting aspects of Roman eye salve is that it was mixed as a paste, then stamped with a seal before being allowed to dry. The seal usually stated the name of the eye doctor (oculist), the kind of salve, and the condition or disease it targeted. The salve was dried to allow for easy storage and transportation. When it was needed, it was powdered and mixed with a liquid again before application.
Hundreds of seals used to stamp cakes of Roman eye salve have been discovered, usually associated with Roman military camps abroad. Here is a four-sided stamp of the oculist Junius Taurus. All four concoctions (Lat. collyria) make use of saffron as an ingredient.
Christing the eyes in revelation in order to "see" the divine. It's the most literal place in the Greek New Testament that uses χριω (εγχριω/egchrio) for transcendent visionary "sight", while obviously mirroring the mystery application of the drugs... showing that the mystery language and practice directly applies to that work, and thus to the practice of those apostles.
It’s the only place in the entire Greek New Testament where a direct medical use of χρ‑ is applied to a bodily orifice-and not just any orifice, but the eyes, the center of perception, vision, and spiritual insight.
18 I counsel you to buy from me gold refined by fire, that you may become rich; and white garments, that you may clothe yourself, and that the shame of your nakedness may not be revealed; and eye salve to apply to your eyes, that you may see.
Applying drug salves to the eyes to induce the spiritual visions that are not normally seen without those salves.
Implication
This passage subtly reverses the expected order:
We know that The Purple was a common (expected) ingredient of the Roman kollourion salve. The kollourion cakes were expected to be purple or dark-purple to indicate potency.
Καὶ κολλύρια δὲ ποιοῦσιν ἐξ αὐτοῦ…
(“And they also make collyria [eye-salves] from it…”)
Here Dioscorides gives recipes for ophthalmic remedies, including saffron, copper compounds, and lead-based powders.
Collyria autem sic fiunt:… cum induruerunt, adservantur; deinde, cum opus est, teruntur et instillantur.
(“Collyria are made thus: … when they have hardened, they are kept; then, when needed, they are ground and instilled.”)
The PGM IV32.12 has a recipe for it…
Λάβε
λευκοῦ ἐλλεβόρου δύο ὀβολούς,
μήκωνος δύο ὀβολούς,
μᾶνδραγόρου ῥίζης δύο ὀβολούς,
κρόκου δύο ὀβολούς·
συλλέψας ταῦτα σὺν οἴνῳ παλαιῷ καὶ χρίσας τοὺς ὀφθαλμούς,
εἰς καθαρόν οἶκον εἴσελθε·
καὶ ὄψει θεοὺς νυκτός περιπατοῦντας
καὶ λέγοντας σοι ἃ ἐὰν θέλῃς.
Take:
Grind them together with old wine,
and, having christed your eyes with this kollourion,
enter a pure room -
and you will see the gods walking about at night
and speaking with you about whatever you wish.”
Remember in the book of Tobit when the sparrow dropped dung in Tobit's eyes, in order that his eyes may be opened as he entered into the sleep of death? Dung is a type of clay used to mix drugs into, that acts as a plaster, to administer the drugs in the eyes of the person.
(9) ἐν αὐτῇ τῇ νυκτὶ ἀνέλυσα θάψας, καὶ ἐκοιμήθην μεμιαμμένος παρὰ τὸν τοῖχον τῆς αὐλῆς, καὶ τὸ πρόσωπόν μου ἀκάλυπτον ἦν.
(9) In that same night, after I had returned (having buried), I slept, defiled, beside the wall of the courtyard, and my face was uncovered.
(10) οὐκ ᾔδειν ὅτι στρουθία ἐν τῷ τοίχῳ ἐστίν·
(10) I did not know that sparrows are in the wall.
καὶ τῶν ὀφθαλμῶν μου ἀνεῳγότων, ἀφώδευσαν τὰ στρουθία θερμὸν εἰς τοὺς ὀφθαλμούς μου,
And while my eyes were open, the sparrows evacuated warm (droppings) into my eyes,
καὶ ἐγενήθη λευκώματα εἰς τοὺς ὀφθαλμούς μου·
and white-films (opaque patches) came-to-be in my eyes.
καὶ ἐπορεύθην πρὸς ἰατρούς, καὶ οὐκ ὠφέλησάν με·
and I went to physicians, and they did not benefit me.
Ἀχιὰχαρος δὲ ἔτρεφέν με ἕως οὗ ἐπορεύθην εἰς τὴν Ἐλλυμαΐδα.
But Achiacharos was maintaining/sustaining me until I went into Elymais.
(8) ἔγχρισον τὴν χολὴν εἰς τοὺς ὀφθαλμοὺς αὐτοῦ,
(8) Christ (smear/apply) the gall into his eyes,
καὶ δηχθεὶς διατρίψει
and, being bitten/stung (e.g. irritated), he will rub/abrade,
καὶ ἀποβαλεῖται τὰ λευκώματα
and he will cast off the white-films,
καὶ ὄψεταί σε.
and he will see you.
(9) προσδραμοῦσα Ἅννα ἐπέπεσεν ἐπὶ τὸν τράχηλον τοῦ υἱοῦ αὐτῆς,
(9) Having run up, Anna fell upon the neck of her son,
καὶ εἶπεν αὐτῷ· Εἶδόν σε, παιδίον, ἀπὸ τοῦ νῦν ἀποθανοῦμαι.
and she said to him, “I have seen you, child; from now on I shall die.”
καὶ ἔκλαυσαν ἀμφότεροι.
and both of them wept.
(10) Τωβεὶτ ἐξήρχετο πρὸς τὴν θύραν καὶ προσέκοπτεν·
(10) Tobit was coming out toward the door and was stumbling,
ὁ δὲ υἱὸς προσέδραμεν αὐτῷ,
and the son ran toward him,
(11) ἐπελάβετο τοῦ πατρὸς αὐτοῦ,
(11) he took hold of his father,
καὶ προσέπασεν τὴν χολὴν ἐπὶ τοὺς ὀφθαλμοὺς τοῦ πατρὸς αὐτοῦ
and he smeared the gall onto the eyes of his father,
λέγων· Θάρσει, πάτερ.
saying, “Take courage, father.”
(12) δὲ συνεδήχθησαν, διέτριψε τοὺς ὀφθαλμοὺς αὐτοῦ,
(12) and they were stung/irritated, and he rubbed his eyes,
(13) ἐλεπίσθη ἀπὸ τῶν κανθῶν τῶν ὀφθαλμῶν αὐτοῦ τὰ λευκώματα.
(13) the white-films were peeled off from the corners/angles of his eyes.
καὶ ἰδὼν τὸν υἱὸν αὐτοῦ ἐπέπεσεν ἐπὶ τὸν τράχηλον αὐτοῦ,
and having seen his son, he fell upon his neck,