Sampling Bags

When collecting sand in the field you need some method of keeping your samples safely separated until you get back to base. There are a number of ways to achieve this but perhaps the most cost effective and easiest way is using self-sealing polythene bags, also variously called zip-lock, zip-seal or mini-grip bags.

These are essentially polythene bags with a re-usable press-to-close zip along one edge, making them ideal for collecting sand samples in the field. They are available in a wide range of sizes from about 38 x 63 mm up to 381 x 508 mm and beyond. My own preference is for bags around 115 x 115 mm, a bit larger than I need but easy to fill and seal. This size of bag easily holds the sample amount I tend to collect, around half a bag full. My own method is to use these sampling bags for temporary storage while collecting in the field.

When collecting samples it is important to label them to prevent samples getting mixed up and this can be done easily by using self-seal bags with write-on panels. These bags come with a single white panel or set of three white panels on one side, designed to allow you to write on them with a pen. A normal biro does work but can easily be rubbed off and a permanent marker pen is more foolproof.

When collecting sand at beaches, and other locations as well, the samples can often be damp or even water-logged and an easy way to prevent your collecting bag from getting wet is to put the water-logged sample into a second bag, sealing them both up carefully. Try not to get any sand particles in the seal or it may leak and carry them upright as well.

When choosing a suitable size to serve as your sampling bags it’s not always best to go for the smallest bag that will contain your sampled quantity. If you try and fill a bag to maximum capacity it will place strain on the seal and the contents are quite likely to spill when the seal fails. Always go for a sampling bag larger than you need. As a guide I never fill a bag more than half full.

Self-seal bags are quite cheap to purchase, costing only a few pounds for batches of 100, the usual quantity sold. A more cost effective option is to shop around and buy them by the 1000. You also have less likelihood of running out of bags when in the field. A 1000 bags can seem quite a lot but it does not take long to use them up when a days collecting can bring home as many as 50 samples.

An important tip when collecting in the field is to make sure you have enough sampling bags with you. When I started collecting I thought that 20 bags was enough but revised this on a recent collecting trip when I gathered 44 different samples. Now, as a rule I carry at least 100 sampling bags with a full pack of 100 more in the car, just in case. You can also collect your samples in rigid containers such as plastic bottles or even glass jars. However, these are heavier and take up more space than cheap polythene bags but are effective none-the-less.

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