Jewelry production in European Middle Ages went through several distinctive phases. In its "early" period that lasted from 500 CE to 1000 CE, Europe remained mostly isolated and troubled with frequent wars, famines and technological stagnation. During that time only few isolated areas managed to maintain some meaningful advancement in jewelry production, most notably British Isles. Age known as High Middle Ages that lasted from 1000 to 1300 CE was marked by ascendancy of Christian Church and the start of Crusades, which finally established contacts to foreign lands and cultures. Two centuries that followed 1300 CE were marked by slow advancement of technology, art and culture, which eventually culminated with the birth of Renaissance.
First 500 years of Middle Ages was dominated by extreme hardship that left majority of western Europe's population fighting for the lives on daily basis. Wars, famine, consecutive waves of plague left several hundred million people dead, and advancement of almost every form of art became stopped or in some cases totally abandoned. The only preservers of art were noblemen, royal families and Catholic Church who managed to safeguard vast quantities of Western Europe wealth. They continued to refine skill of jewel making (most commonly golden items with connections to Church), especially by continental Celts and Anglo Saxons on British Isles. General population however continued to sporadically use jewel items made from simple materials and semi-precious gemstones, often carried because of specific superstitious beliefs for warding off evil and disease. By 9th century jeweled weapons, chalices and more simple jewels designs became slowly more available to the general population, especially made by Celts and Anglo Saxons (who were by that time heavily invested in defending their lives against frequent Viking invasions).
Eastern Europe on the other hand retained stability that was provided by the Byzantine and later on Ottoman Empire. Unaffected by plagues and constant wars, artisans continued to improve their craft and were more than ready to showcase their advanced designs when the rest of the Europe entered into Renaissance.
General stability that was brought after the 1000 CE enabled the resurrection of many long disused art forms, including jewel making. Byzantine , Anglo -Saxon, Germanic and Gothic styles were able to more freely travel over Europe and influence local population and artisan into fast adoption of new styles and decorations. By the times of Crusades (11th-13th century) Slavs, Magyars and Vikings were completely converted to Christianity which enabled easier sharing of art and advancement of technology across entire Europe. By the end of 13th century, rise of the middle class brought the wealth and art to the general masses and enabled Europe to prepare itself for the birth of Renaissance and the quick expansion of European settles across entire world.