The sequence in which you add materials to a formula changes the formula. This is not a minor procedural detail. It is chemistry.
Blending order in perfumery refers to the sequence in which aromatic materials are added to the formula during construction. The established principle — practised across both craft and industrial perfumery — is to build from the heaviest (least volatile) materials to the lightest (most volatile).
In practice this means: base note materials first (resins, musks, fixatives, heavy woods), then heart note materials (florals, spices, green notes), then top note materials (citrus, light herbs, aldehydes), with the alcohol carrier added last or in stages.
The rationale is chemical: heavy base materials interact differently when added to an existing accord than when used as a primary vehicle. Adding a drop of bergamot to a sandalwood-patchouli base gives a different result than adding sandalwood to a bergamot solution. The heavier material grounds the formula. The lighter material responds to the environment it enters.

FACTS
Aftel (Essence and Alchemy) documents blending sequence as a fundamental craft variable in natural perfumery: she builds from the base outward, establishing the structural accord before introducing heart and top notes, and observes that reversing this sequence typically produces a less integrated result.
The Northwest School of Aromatic Medicine (Core Principles of Perfume Formulation) confirms that the 30-30-30 formulation framework is executed sequentially — base materials are assessed for balance first, heart materials added and reassessed, top notes introduced last.
RSC Chemistry of Fragrances explains the chemical basis: in solution, high-boiling-point compounds change the solvation environment for low-boiling-point compounds. Sequence affects molecular interaction, and molecular interaction affects odour character.

TAKEAWAY
Build base first. Always. Establish the structural anchor — the fixatives, the resins, the musks — before introducing the volatile layers above them. If you add a bright top note to an unfinished base, you are evaluating the wrong thing. The top note will distort your perception of what the base needs.
Finish the foundation.
Then build upward.
Then add the alcohol.
Then macerate.
Sequence is not ceremony. It is method.