primers

Primers are terms used across several fields to denote an initial component that triggers or supports a subsequent process. Common usages include biology, materials, ammunition, and cosmetics.

In molecular biology, DNA primers are short single-stranded oligonucleotides that define the start (and sometimes end) points for DNA synthesis. They are typically 15–30 nucleotides long and must be complementary to sequences flanking the target region. Primers are used in PCR, DNA sequencing, and cloning. Key design considerations include specificity to the target, appropriate melting temperature, balanced GC content, and minimal formation of primer dimers or secondary structures.

In surface finishing, a primer is a preparatory coating applied to a surface before paint or other finishes. Primers improve adhesion, provide a uniform base, and block stains or metals from bleeding into the final layer. Types include metal primers, alkyd, acrylic, and epoxy primers, chosen according to substrate and environmental exposure.

In firearms and ammunition, a primer is a small explosive charge housed in the cartridge that initiates ignition. When struck by the firearm’s hammer or firing pin, the primer ignites, transferring flame to the propellant and starting combustion. Modern primers are designed for reliable ignition and safety; variations include boxer and non-boxer designs.

In cosmetics, a makeup primer is a product applied to the skin before foundation to create a smooth base, minimize the appearance of pores, control shine, and extend wear. Formulations vary and may be silicone-based, water-based, or hybrid, with options for skin tone, color correction, or moisture retention.