29 July 2015
Tissue is present in the everyday lives of almost everyone on the planet. With so many variations, it has to be one of the most widely manufactured and produced commodities, so why does some tissue paper say high quality and seem more appealing to a purchaser? Very simply, the appearance of the tissue tells us everything we need to know about quality. If there is a choice between white toilet paper or grey toilet paper, the white toilet paper is chosen as it appears cleaner and of a higher quality, visually. Public perception of appearance then tells us that it is vitally important to uphold the visual appearance and quality of the product to maintain the high standards of tissue produced, regardless of what form it is in.
When talking of measuring appearance, the first question to ask is what form does the tissue take? Are we talking about toilet tissue? Kitchen roll? Napkins? Or a simple box of tissues, present in almost every household?
The measurement for all of these different variations of tissue are all invariably similar but there can be different variations in measurement method that could be addressed, depending on individual company manufacturing processes.
It is important to be thinking of the instrument that would be needed to make the desired measurements whilst answering the questions below, but we will discuss the possibilities later on.
To measure a sample of the tissue, you first need to decide what sample you are measuring. For the sake of example, we will be looking at toilet tissue. This is a product widely available to members of the public and this fact must be remembered when considering the following points during measurement method.
How big should my sample size be?
All instruments come with a measurement area that can vary in size and can accommodate sample sizes of up to two inches in diameter and as small as ¼ inch in diameter. This variation in size can offer a choice of method however, if regular testing is going to be done, particularly if some of the samples are smaller or larger than normal, it is important to take measurements with the same size measurement port to allow for consistency and accurate results. If measurements were being taken with a 1 inch port and another sample is measured using a ½ inch port, even if they were from the same batch, the results would differ due to the amount of light energy able to be shone at the sample.
How thick should the sample be?
As some toilet tissue is made up of layers, there is a choice of measuring a single layer or the product as a whole. The ideal method would be to measure a thicker sample section of multiple sheets as, when being viewed by a member of the public in a shop, they are seeing the toilet paper on a roll, rather than as individual sheets. It makes sense then, to base the measurements on what the customer will be seeing rather than going too in depth in a laboratory setting.
To accurately receive the true colour of the samples and to keep the method the same continuously, a certain number of sheets should be measured every time. This number would depend entirely on the quality of the toilet tissue and quantity available but should be enough that it presents an opaque surface for the reflected colour to be measured.
Is taking an average necessary or will a one off measurement suffice?
This would depend on how accurate you wish to be, how many samples need to be measured, how uniform the sample appearance is and how much time can be spent on quality control processes. One method could be to get the opaque sample and take an average measurement across the entire sample, such as 6 measurements taken at different points on the sample. If the sample is coming from the same batch, it could be feasible to take one measurement of a sample and then take a measurement of another sample of the same batch.
What type of lighting should the samples be measured under?
In the average supermarket where mass quantities of toilet tissue are sold, fluorescent lighting is used. In an average household, incandescent lights are used. Are appearance measurements taken using fluorescent, incandescent or any other lighting type? This would be at the discretion of the manufacturer and where the product is going.
Has the sample been optically brightened?
A sample that has been treated with an optical brightener will absorb light more in the ultraviolet region and emit light in the blue region of the spectrum, making products appear whiter. This must be taken into account when measuring appearance.