A dental drill or a carborundum paper is used in the pretreatment of shell exteriors.When the visible contaminants have already been removed, the samples for carbon dating are then reduced in size by an applicable method to increase the surface area before further pretreatment.Labeling of bone samples with animal glue is an example of artificial contamination.Other contaminants that may be introduced during sample collection and packaging are biocides, conservation chemicals like polyvinyl acetate and polyethylene glycol, cigarette ash, and labels and wrappers that are made of paper.Contaminated samples, naturally, will have inaccurate results.The specific effect of the contaminant on radiocarbon dating results depends on the type of contaminant, the degree of contamination, and the relative ages of the sample and the contaminant.This occurrence can make the samples seem younger than their true age.
Artificial contamination refers to the introduction of contaminants by man during the collection, field conservation, or packaging of the samples.
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.
There are two types of pretreatment usually applied to samples for carbon dating—physical and chemical.
The physical pretreatment of samples for radiocarbon dating is generally done by removing contaminants without the use of chemicals followed by the reduction in sample size.