You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Normans

Context:
Various princes of the Holy Land arrived in Limassol at the same time, in particular Guy de Lusignan. All declared their support for Richard provided that he support Guy against his rival Conrad of Montferrat. The local barons abandoned Isaac, who considered making peace with Richard, joining him on the crusade, and offering his daughter in marriage to the person named by Richard. But Isaac changed his mind and tried to escape. Richard then proceeded to conquer the whole island, his troops being led by Guy de Lusignan. Isaac surrendered and was confined with silver chains, because Richard had promised that he would not place him in irons. By 1 June, Richard had conquered the whole island. His exploit was well publicized and contributed to his reputation; he also derived significant financial gains from the conquest of the island. Richard left for Acre on 5 June, with his allies. Before his departure, he named two of his Norman generals, Richard de Camville and Robert de Thornham, as governors of Cyprus.

Question:
What were Isaac's chains made out of?

silver