Design patterns are best practices for known problems in a specific context. Many patterns have been proposed in different domains, such as object-orientated programming, software architecture, and workflows, to name a few. However, blockchain interoperability is a recent area of work and, to our knowledge, no design patterns have been defined yet. The purpose of this work was to identify blockchain interoperability patterns that may exist in blockchain interoperability solutions. We identified six patterns through the observation of 35 interoperability solutions. A specification was built for each pattern using the Alexandrian template. The specification was evaluated with five semi-structured interviews with blockchain experts to collect data on the comprehension, completeness, and utility of the patterns. The results show that all interviewees identified the patterns. However, the pattern specification has different degrees of confidence in terms of clarity, completeness, and utility. Finally, all interviewees thought that the proposed patterns may be helpful to software architects in their first blockchain interoperability project.