In general, infinite-age contamination can make a sample considerably older while modern contamination can make the sample significantly younger than its true age.

Regardless of the carbon dating methodology employed, be it radiometric dating or the accelerator mass spectrometry (AMS) method, a process must be done before analysis to get rid of all possible contaminants. Radiocarbon dating labs receive various materials for analysis but not all portions of the samples can be used.

Natural contamination pertains to the introduction of contaminants to the sample by its surrounding material.

Materials such as charcoal, wood, peat, and textiles typically undergo the acid-alkali-acid (AAA) method before radiocarbon dating.

Learn more Materials such as sediments and soils typically undergo acid washes (no alkali) before radiocarbon dating.

One of the basic assumptions in carbon-14 dating is that the sample being analyzed has undergone only radioactive decay and has remained unaltered by any other process over the years since it ceased interaction with the biosphere. The archaeological artifacts and geological specimens sent to labs for radiocarbon dating are usually found embedded or buried with other materials that may have affected their radiocarbon content.

Any carbon-containing material that affects the carbon 14 content of any given sample is therefore a contaminant.

Metal and stones cannot be directly dated unless they have organic materials embedded in them.

There is no standard method for pretreatment applicable to all samples for radiocarbon dating.

The effect of these organic acids on the sample, whether they would make the sample older or younger, depends on the age of their original organism.

When roots of plants penetrate wood, charcoal, soil, or bones, modern carbon is already introduced to them.

Limestone is of geological origin and would be much older than any archaeological sample; hence, inclusion of limestone during the carbon 14 dating would make the sample older than its true age.

Humic and fulvic acids are naturally present in soil where microbial degradation of plants and animals has occurred.

Physical pretreatment usually involves the removal of rootlets that intruded on the sample using tweezers or forceps.