A method and a device for the control of a joint between a first element (18) and a second element (21). The first element preferably is an end element of a container and is inserted in an opening in said container such that a rim is formed around the opening and includes a joint (16). The rim allows the placement of a radiation or wave energy transmitting source (13) at one side thereof and a detector device at the other side. The radiation or wave energy source has a capacity of penetrating, preferably fully, the rim and illuminating said rim by a small dot (14), which is scanned crosswise the width of the joint by a scanner device. The container (10) is rotated around an axis (12) and the detector device (22) registers the characteristics of the radiation that passes the joint and/or is reflected at the joint and which originates from a repeated "point illumination of the joint". By placing the detector device at a sufficient distance from the rim there is obtained a magnifying effect in the detector, which allows the detection of very small changes in the quality of the joint. The method and the device are especially suited for joints comprising substantially plastics material and where the product, which may affect the joint also substantially consists of an organic material, for instance a food product.
