var
 S: TBlobStream;
 B: pointer;
 c: integer;

...

 Table1.Edit;
 S := TBlobStream.Create(Table1BlobField as TBlobField, bmWrite); {кажется, так}
 C := S.write(B, C);
 Table1.Post;
 S.Destroy;

var
 S: TMemoryStream;
 B: pointer;
 C: integer;

...

S := TMemoryStream.Create;

...

 Table1.Edit;
 S.Clear;
 S.SetSize(C);
 C := S.write(B,C);
 (Table1BlobField as TBlobField).LoadFromStream(S);
 S.Clear;
 Table1.Post;

...

S.Destroy;