Which cannot save themselves from rust and corrosion: Which refers back to the idols, not to the materials of which they were made. Save themselves from means “keep [or, protect] themselves from.” Rust is not technically correct, since rust forms only on iron. “Tarnish” (so Good News Translation) is a better word; it can refer to discolored silver. The Greek word here also refers to the green coating that discolors copper. Some idols were cast in bronze and overlaid with gold or silver. Perhaps this is what the writer is referring to. The meaning of corrosion is discussed in the paragraph below.

When they have been dressed in purple robes is a clause ambiguously placed in Greek. It can be taken with the following sentence (Revised Standard Version, New Revised Standard Version, Contemporary English Version, New Jerusalem Bible, Traduction œcuménique de la Bible) or with what comes before it (Good News Translation, New American Bible, New English Bible, Moore). How we understand the Greek word that Revised Standard Version renders corrosion will determine which of these two connections is correct. Literally the word means “food.” A textual problem lurks behind this word, but basically the text is saying the idols cannot save themselves from being eaten. Revised Standard Version seems to take this term as referring to metal being eaten away by using corrosion (which is similar to the term it renders as rust), although how gold or silver can be described this way is not clear. Good News Translation “termites” assumes that the woodwork of the idols is being eaten away by termites. New English Bible and Moore translate “moth[s].” (This can partly be explained on the basis of the textual problem just mentioned; compare Matt 6.19-20.) But moths attack cloth, so both New English Bible and Moore, like Good News Translation, reorder the verse so that the purple robes clause comes before the rust and corrosion clause. This way the moths are seen as attacking the purple robes. New Jerusalem Bible says “woodworm” and New American Bible has “insects,” which may be the best solution of all.

The translator must understand that the Greek word used here does not literally mean “termite,” “insect,” “corrosion,” or “moth” (though it is possible the Hebrew original had “moth”). It means “food.” The various translations are interpreting it in somewhat different ways, but they all amount to saying that the idols cannot protect themselves from being eaten away by something or other. The translator will probably feel more comfortable and the readers less puzzled if the two clauses of this verse are reversed, as in Good News Translation, and the problematic noun is translated as “insects” or as some particular insect known to devour wood or cloth.

Purple goods were a sign of wealth or distinction. Compare Jdg 8.26; Est 8.15; 1 Macc 8.14. A Handbook on the Gospel of Mark suggests ways for translating the color purple. In brief, translators are urged to take one of four possible approaches (in order of preference):
(1) select an indigenous term that is approximately the color of purple or red-blue;
(2) find an approximation of the color, employing other terms that identify colors that are quite close; for example, “dark red,” “burnt red,” and so on;
(3) identify the color purple through the color of some bird or flower; for example, “cloth dyed with the color of…”;
(4) use a phrase identifying the process of dyeing cloth, for example, “cloth like that dyed in…,” and then introduce the proper plant in the culture that is used for dyeing cloth or other materials with a purple color.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on The Shorter Books of the Deuterocanon. (UBS Helps for Translators). New York: UBS, 2006. For this and other handbooks for translators see here.

Whatever is done for them is false: The translation must make it clear that them refers to the idols, not the women referred to in verse 43. The Good News Translation rendering of this sentence, “Everything about these idols is false,” is an equally good translation of the Greek. New American Bible has an interesting approach: “All that takes place around these gods is a fraud.” This is not only a justifiable translation of the Greek text, but it also relates the verse to the verse just before it. Another way to say this is “Everything that happens around these idols is false.”

A more difficult problem for some translators may be finding an appropriate equivalent for the term false. The worship of these idols is useless, vain, without value. Contemporary English Version follows this interpretation with “Everything the Babylonians do to serve their idols is useless.” New English Bible attempts to round out the meaning with two descriptive nouns, “fraud and delusion,” where the fraud is on the part of the priests and the delusion is on the part of the worshipers.

Why then must any one think that they are gods, or call them gods?: This occurrence of the refrain is almost word for word the same as in verse 40. The difference in Greek is altogether too minor to be reflected in translation.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on The Shorter Books of the Deuterocanon. (UBS Helps for Translators). New York: UBS, 2006. For this and other handbooks for translators see here.