Exode 30:34

And the Lord said to Mosheh, Take to thee spices, balsam, and onycha, and galbanum, choice spices, and pure frankincense, weight for weight shall it be.

TAKE UNTO THEE ‘SAMIM’ (AROMATICS), STACTE, AND ONYCHA, AND GALBANUM; ‘SAMIM’ (AROMATICS) WITH PURE FRANKINCENSE. Rabbi Abraham ibn Ezra commented that by way of the plain meaning of Scripture the interpretation of the verse is: “take unto you the aromatics which are stacte, onycha and galbanum; these spices [you are to take], and pure frankincense with them.” But it is not correct that Scripture should just repeat the word samim [in such a short verse], for it is not the normal way of Scripture to repeat words unless there is some lengthy interpolation or in order to indicate that it is a continuing thing. The truth is as our Rabbis have said, that the second word samim refers to other aromatics.
Now Rashi wrote: “‘Samim’ — the least number of aromatics implied by the plural form of this word is two. Stacte, and onycha, and galbanum, make together five. ‘Samim’ adds a similar number to those already prescribed, thus making ten. With frankincense, makes eleven [altogether].”
But one wonders! Why did Scripture not mention them explicitly? Perhaps Scripture is saying: “Take unto thee aromatics, stacte, and onycha, and galbanum, many aromatics with pure frankincense,” thus insisting only on these four spices, for they were the ones that caused the cloud of the smoke of the incense to ascend; but He commanded that they add to them many other aromatic spices in order that the pillars of smoke [of the incense] should be fragrant. This is why He did not explain [in the case of the incense] the weight of each component [as He did in the case of the Oil of Anointment], nor how much of it should be burnt [daily], since He insisted only that these four [spices mentioned] should be alike [in weight], and that he should add to them other good spices for the burning. The reason for this is that just as He had said with reference to the Oil of Anointment that they make it in accordance with the art of the perfumer, and did not specify how it was to be made but relied upon it [that they knew how to make it], so He said in respect of this incense that he take an equal weight of these four [mentioned] aromatics, and add to them other aromatics and make out of all the components one incense, done after the art of the perfumer, [which implies by] using spices known to blend well with these [four] and by preparing them through the process by which they are usually prepared. It is of this …

סמים; we explained this already earlier. (where?)

סמים ולבונה זכה, according to the plain meaning, the Torah first describes the ingredients used for the incense in a general manner, before listing each individually. There follows a description of precisely what was included in the general term סמים. נטף ושחלה וחלבנה, stacte, onycha and galbanum, these are fragrant herbs which I commanded you to use. In addition, you are to take pure frankincense; According to the plain meaning of the text לבונה זכה is not to be counted as one of the spices, fragrances, listed, but the word סמים after the list נטף, שחלה, חלבנה concludes the list of the spices. It is the custom of the Torah to repeat something which had been used as a heading for an introduction when that particular part of the subject has been concluded. We find an example of this in Genesis 9,17 when G’d concluded a covenant with Noach involving the rainbow. He said זאת אות הברית, “this is the sign of the covenant,” both in 9,12, and again in 9,17.

קח לך סמים, the ones already mentioned in connection with the oil of anointing in verse 23-24 plus the three mentioned in this verse, i.e. נטף, שחלה, חלבנה, and in addition to these some other spices known to act as improving the mixture of those already listed. According to our sages in Keritut 6 Shibbolet, Nerd, Karkom and Kosht were such spices which when blended in with the ones listed in the Torah already would provide the balance of fragrance the Torah wanted to achieve. [The problem facing commentators is the fact that even when we add all the spices or oils mentioned in this chapter together, even assuming that frankincense is one of them, we only arrive at a total of eight, whereas traditionally there were supposed to be 11 as we mention in our daily prayer of Pittum haketoret. Ed.]

ולבונה זכה, this pure frankincense did not need to be mixed with any other ingredient to achieve the Torah’s purpose as part of the incense. This helps us arrive at the number 11 our sages state were contained in the mixture presented on the golden altar.

בד בבד, “each is to have the same weight.” (customary translation) The Talmud, tractate k’ritut folio 5 understands this expression as based on the word בדד, “separate, isolated,” i.e. each individual unit of spice should have the same weight. The Talmud even discusses if when weighing it, it suffices to note that both scales of the scales are at the same level, or if the spice in question must actually tip the scale downwards a little. They also discuss if, as is customary, a stone or equivalent which had proved to be of the required weight can be used for weighing the next quantity of spice, or if each spice has to be weighed independently without any weights being used. According to Rashi in the Talmud there, weights must not be used instead, only spices must be placed on the scale. Our author does not understand why the use of weights should have been forbidden.